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  • 1990-1994  (395)
  • 1991  (395)
  • Computational Chemistry and Molecular Modeling  (394)
  • Nuclear reactions
  • 101
    Electronic Resource
    Electronic Resource
    Algebrants in many electron quantum mechanics. II. New computational algorithms (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 225-234 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Algebrants are generalized matrix functions; they are multilinear forms of which the determinant, the permanent, and the immanant are special cases. A formal definition and fundamental properties of algebrants was given in paper I of this series. The present work develops algorithms for computation of those algebrants that arise in computational spin-free quantum chemistry for valence bond (VB) wave functions built on nonorthogonal orbitals. Namely, we exploit the left- and right-hand antisymmetry of N P N ˚A to develop algorithms that greatly reduce or eliminate the N! problem. The algorithms can be implemented in any computer language; our implementation in FORTRAN is available upon request. The savings effected by spin-free vs Slater determinant versions of VB theory are illustrated for 2, 3, …, 10 electrons.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400823
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  • 102
    Electronic Resource
    Electronic Resource
    Analysis of the density-gradient-expansion approximation for the exchange-correlation energy of density-functional theory (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 235-248 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To understand the density-gradient expansion approximation for the exchange-correlation energy of density-functional theory from a fundamental viewpoint, we have performed an analysis of the corresponding expansion of the Fermi-coulomb hole charge distribution. The Fermi-Coulomb hole represents the correlations between electrons resulting from the Pauli exclusion principle and Coulomb's law. The analysis is performed in the exchange-only approximation by considering the expansion for the Fermi hole to terms of O(▽3) as applied to atoms. Our study shows that the expansions to O(▽), O(▽2), and O(▽3) all severely violate the constraint of positivity, becoming progressively worse with increasing orders of ▽. Further, the expansion to O(▽2) also severely violates the constraint of charge neutrality. (Terms of O(▽) and O(▽3) do not contribute to this constraint or to the exchange energy.) Thus the description of the physics of Pauli correlations in atoms as given by this approximation is highly unphysical. In spite of this, the exchange energy to O(▽2) is superior to the local density approximation because the expansion hole better approximates the exact Fermi hole in the interior of atoms from which arise the principal contributions to the energy. However, the improvement is not substantial, as the oscillations in the expansion Fermi hole occur within the atom itself. For asymptotic positions of the electron, the expansion holes to each order neither approximate the local density approximation nor the exact Fermi hole. Thus we understand why the expansion cannot lead to accurate highest occupied eigenvalues. The oscillations of the expansion Fermi hole also demonstrate why the Slater potential and electric field that result from these hole charge distributions are singular. On the other hand, we show that the expansion approximation is mathematically consistent in that the coefficient of the gradient correction term for screened Coulomb interaction to O(▽2) as obtained from the approximate Fermi hole is the same as that derived from linear response theory. We conclude with remarks on the Coulomb hole as obtained within this gradient expansion approximation scheme.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400824
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  • 103
    Electronic Resource
    Electronic Resource
    Calculation of the total atomic binding energy with recently proposed kinetic-, exchange-, and correlation-energy functionals (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 261-268 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The functionals adopted in the present work are those of DePristo and Kress [Phys. Rev. A35, 438 (1987)] for the kinetic energy, of Cedillo et al. [Phys. Rev. A38, 1697 (1988)] for the exchange energy, and of Wilson and Levy [Phys. Rev. B41, 12930 (1990)] for the correlation energy. In addition to the kinetic-, exchange-, and correlation-energy functionals, the total-energy functional used in the present calculations contains also the functional describing the interaction of the electrons with the atomic nucleus, and the functional describing the classical or direct part of the interaction among the electrons. Using these functionals, a two-parameter and a three-parameter variational density-functional calculation of the total atomic binding energy of the Ne atom is carried out. The electron (number) density of the Ne atom is modeled by using hydrogenlike one-electron radial wavefunctions (with the 2s radial function orthogonalized to the 1s radial function) containing two/three variational parameters. It is found that the calculated correlation energies are in reasonable agreement with the correlation energy value obtained from the Wilson and Levy expression with a Hartree-Fock electron density.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400826
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  • 104
    Electronic Resource
    Electronic Resource
    Application of local-density functional theory to molecules containing a hypervalent bond (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 269-279 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular and electronic structures of ADPO 1, a model thiapentalene 2, and [Xe2F3]+ have been calculated in the local-density functional (LDF) formalism with polarized double numerical basis sets. The molecules were calculated to have planar C2ν structures in agreement with experiment and in contrast to Hartree-Fock molecular-orbital calculations. The vibrational spectra of all species were calculated to show that the optimized structures are indeed minima. The calculated spectrum of [Xe2F3]+ is compared with the experimental one and excellent agreement is found. These results demonstrate that the LDF method can be applied to the prediction of molecular structures containing hypervalent bonds.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400827
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  • 105
    Electronic Resource
    Electronic Resource
    Nonadiabatic molecular dynamics (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 299-309 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular dynamics simulation of mixed quantum-classical systems, in situations where the quantal degrees of freedom undergo transitions among states, poses a number of challenging problems. Among the difficulties are bifurcation of trajectories that evolve into different quantum states and proper treatment of quantum coherence. In this article we outline the problems and contrast the ways in which they are addressed by current methods for nonadiabatic molecular dynamics. In the course of this comparison we present a new result, the relationship between the velocity adjustment in the “surface hopping” method and the “Pechukas force,” as well as some new reflections on an old result, oscillatory yields in ion-surface scattering.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400830
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  • 106
    Electronic Resource
    Electronic Resource
    Density-functional theory of the superconducting state (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 289-297 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A density-functional theory describing the superconducting state of matter is presented. The formalism leads to a set of single-particle equations that are structurally similar to the Bogoliubov-de Gennes equations but (in contrast to the latter) incorporate both normal and superconducting exchange-correlation effects. It is demonstrated via a rigorous decoupling scheme that these single-particle equations are equivalent to a set of normal Kohn-Sham equations, and a BCS-type gap equation to be solved self-consistently with the Kohn-Sham equations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400829
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  • 107
    Electronic Resource
    Electronic Resource
    Path integral approach to chemical dynamics: A test case of H + O2 ↔ OH + O reaction (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 311-323 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Determining mechanisms of chemical reactions involves finding dynamical paths between desired (given) reactant and product states. We have developed a method that is based on recasting the principle of stationary action into a general and computationally tractable form that yields all dynamical paths connecting the initial and final configurations of the system. Thus the method has advantages over the traditional initial-value trajectory calculations for solving such boundary value problems. We give some examples of reaction paths for H(2S) + O2(3Σg-) ↔ OH(2II) + O(3P) on the ground state potential energy surfaces HO2(2A″).
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400831
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  • 108
    Electronic Resource
    Electronic Resource
    Ion solvation energies from density functional theory (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 281-288 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electrostatic solvation energies of singly charged monoatomic ions may be predicted from the knowledge of an electrostatic potential buildup from a physically meaningful ionic radius. Since the asymptotic behavior of the electrostatic potential for cations and anions do not follow the same pattern, different methodologies are needed. The reaction field potential required for the calculation of Born's solvation energies of singly charged cations may be obtained from the simple Thomas-Fermi-Dirac theory, based on the condition that the electrostatic potential of the ground-state atomic ions do exactly equal the negative of their chemical potentials. For singly charged anions, electrostatic solvation energies may be directly obtained from Sen-Politzer electrostatic potentials. Numerical results are presented for two representative series of ions and compared with experimental data.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400828
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  • 109
    Electronic Resource
    Electronic Resource
    Electrophilic substitution in the benzofuran series: A theoretical (AM1) study (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 325-333 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrophilic substitution in a series of 5-aminobenzofurans was investigated by all-valence electron AM1 molecular orbital calculations. Various molecular properties of the reactants, intermediates, and products were computed and compared with available experimental data. The results indicate that while calculated ground-state charge densities cannot be used to predict reactivity and orientations, the relative thermodynamic stabilities of the reaction intermediates (arenium ions, σ complexes) reflected by calculated heats of formation (ΔHƒ) accurately indicated the isomers resulting from the kinetically controlled substitutions. The relative stabilities of the reaction products could be used to predict reaction preferences for the thermodynamically controlled electrophilic substitutions. Positions 4 for both aniline and 5-aminobenzofurans were the most susceptible toward electrophilic attack. The calculated ΔHƒ of the reaction intermediates, in good agreement with the experimental data, were capable of distinguishing between slightly nonequivalent positions such as the ortho and ortho prime to a substituent. Calculated AM1 ΔHƒ may represent practical guides in the prediction of sites of electrophilic aromatic substitutions for molecules with complex structures.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400832
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  • 110
    Electronic Resource
    Electronic Resource
    Intermolecular dynamics for weakly bound donor-acceptor complexes (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 347-358 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have performed ab initio (3-21 G) calculations on the weakly bound donor-acceptor complex between benzene and tetracyanoethylene (TCNE) as a function of various intermolecular motions. The resultant potential energy surface (PES) was then fit to the product of analytical functions. Classical dynamics was performed on this PES by solving Hamilton's equations using a fourth-order Runge Kutta differential equation solver. Time steps were of the order of 1.0 femtosecond and the system was allowed to evolve for 1,000,000 time steps. Fast Fourier analysis of the resulting trajectories indicate that the primary intermolecular vibrational frequencies are 118, 228, and 232 cm-1. These correspond to the motion of the intermolecular separation coordinate, and the two twisting coordinates. We also discuss other possible solutions, zero-point energies, etc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400834
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  • 111
    Electronic Resource
    Electronic Resource
    On molecules and ions in strong magnetic fields (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 371-385 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Some of the fundamental theoretical concepts for molecules in homogeneous strong magnetic fields are discussed. First, we perform the pseudoseparation of the center of mass motion for neutral as well as charged systems. The resulting Hamiltonian allows us to investigate the problem of the Born-Oppenheimer adiabatic separation of electronic and nuclear motion in the presence of a magnetic field. In particular, we study the most important differences to the field-free case. Finally we discuss the symmetry groups for molecules in a magnetic field and investigate the possibilities and effects of the interaction of molecular electronic states through nuclear motion. Even for diatomic molecules severely enhanced nonadiabatic effects may occur in a magnetic field.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400836
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  • 112
    Electronic Resource
    Electronic Resource
    Shape analysis along reaction paths of ring opening reactions (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 335-345 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this work we analyze the interrelations between potential energy changes and molecular shape changes along the reaction paths for a series of ring-opening reactions. The processes studied correspond to the opening of the four-member rings of 1,2-dioxete, 2H-oxete, 2H-thiete, and 1,2-dithiete, which recently have been given considerable attention in the literature. We describe the molecular shape in terms of a continuum of fused-sphere surfaces, which are characterized by using molecular topological methods. The four processes cover a range of reaction enthalpies from largely exothermic to almost thermoneutral. The similarity between the configurations found along the reaction path is assessed quantitatively in terms of parameters associated with the molecular shape and the path itself. We find a correlation between the value of the energy barriers (and reaction enthalpies) and the similarity parameters. The correlation is comparable to that found in the case of various other processes, such as torsional changes, collisions, and intramolecular atom displacements or shifts. The results are in line with the intuitive correlations expected from the Hammond postulate.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400833
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  • 113
    Electronic Resource
    Electronic Resource
    Kinematic distribution function to calculate rotational populations of photofragments from photodissociation of triatomic molecules (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 359-370 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general procedure to evaluate the rotational state population distributions of the nascent photofragments from the photodissociation of polyatomic molecules has been implemented with the use of the kinematic distribution function developed by Chen and Pei [Chem. Phys. Lett. 124, 365 (1986)]. Numerical evaluations of rotational state population distributions of diatomic photofragments from photodissociation of the general class of triatomic molecules are presented. The calculated rotational state population distributions are compared with the most recent experimental data on OH and SH photofragments to obtain the information on the kinematic aspects of the photodissociating H2O and H2S molecules.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400835
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  • 114
    Electronic Resource
    Electronic Resource
    Atoms and ions in intense magnetic and electric fields (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 401-414 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The study of atoms and ions in unusual environments is an area of current interest. Examples of such environments are the Crab pulsar, where magnetic fields well in excess of 1012 G are encountered and plasmas, studied under intense laser irradiation, where “confined” atoms are subjected to electric fields corresponding to laser fluxes of 1018 W/m2. In this article, a unified theoretical approach is presented to treat atoms in such intense fields. The major theoretical tool employed is the Bloch or canonical density matrix. This is used first for treating magnetic fields, numerical examples of heavy atoms, and ions in intense fields being referred to specifically. Then the same theory is used for “confined” atoms in intense electric fields. Very brief reference is made to molecules in magnetic fiels, with the illustrative example of the simplest molecular ion H2+.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400838
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  • 115
    Electronic Resource
    Electronic Resource
    Single-active electron calculation of multiphoton process in krypton (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 415-429 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We employ a method for solving the time-dependent Schrödinger equation for an atom or molecule in an intense, pulsed-laser field to study multiphoton emission processes. Single-electron effective potentials have been developed that reduce the computational effort required for multielectron systems. Illustrative results for electron and photon emission rates from krypton at 532 nm in the intensity range (1-4) × 1013 W/cm2 are presented and compared to recent measurements.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400839
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  • 116
    Electronic Resource
    Electronic Resource
    Time-Resolved magnetic field effects in the recombination products of geminate triplet pairs for electron phototransfer reactions (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 387-399 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We studied the influence of the additives of tetracyanoethylene (TCE) (radical-anion acceptor) and the variations in exciplex concentration on the magnitude of time-resolved magnetic field effect in a delayed excimer fluorescence in polar exciplex system pyrene-N,N-diethylaniline. The nonmonotonous dependence of the magnetic field effect on tetracyanoethylene concentratration was found. The magnitude of the magnetic field effect was brought close to the predicted maximum limit of about 300 ns by decreasing the exciplex concentration. We conclude that the yield of the triplets, resulting from intercombination transitions in a singlet exciplex, is rather small. The upper limit for the rate constant of these transitions has been determined to be less than 4.6 × 106 s-1.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400837
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  • 117
    Electronic Resource
    Electronic Resource
    Hund's second rule and the electronic structure of transition-metal oxides (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 431-440 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An orbital polarization (Hund's second rule) correction to local spin density (LSD) theory is developed in both a spherical harmonic basis and in a crystal field basis, and applied to the electronic band structure of FeO, CoO, NiO, and La2CuO4, resulting in a substantial enhancement of the LSD insulating band gap for NiO, and the creation of insulating band gaps for FeO, CoO, and La2CuO4.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400840
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  • 118
    Electronic Resource
    Electronic Resource
    Variational calculations on ammonia using two symmetrical normal modes (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 441-450 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Variational calculations have been carried out on the ammonia molecule using two-dimensional potential energy functions. The two dimensions used are the inversion and symmetrical stretching coordinates. If the potential function includes a term to describe the interaction between these two coordinates, the results are as good as those obtained in other studies using a six-dimensional potential function. The barrier height for the new potential function is 1857.5 cm-1.
    Additional Material: 10 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400841
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  • 119
    Electronic Resource
    Electronic Resource
    Theoretical and experimental study on small molecular ions. I. Ab Initio calculations on CSe, CSe+, and HCSe+ species (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 451-459 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio molecular-orbital calculations were carried out on carbon monoselenide (CSe), its cation CSe+, and the selenoformyl cation HCSe+. Equilibrium- and transition-state geometries on the potential energy surfaces (PES) were located at the HF and MP2 levels using a valence double-ζ (d, p) basis set on H and C and the Huzinaga valence triple-ζ (d) basis set on selenium, respectively. The global minimum on the HCSe+ (PES) is the linear species 3 with the dissociation energy towards H and CSe+ of 151.5 kcal mol-1 (MP4//MP2 + ZPE level). While at the HF level the strongly bent isomer 4 is a local minimum structure lying 67.8 kcal mol-1 above 3 and separated from 3 by a small barrier of 6.2 kcal mol-1, MP2 geometry optimizations suggest that CSeH+ isomer is unstable.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400842
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  • 120
    Electronic Resource
    Electronic Resource
    Photoelectron spectra of halogenofurans (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 479-487 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The UV photoelectron spectra of 2-halogenofurans, together with 3-iodo and 2,5-diiodofurans, have been studied. The assignment of the lower energy region of the spectra was based on correlation of the ring π- and halogen levels in the related compounds, resolved vibrational structure, and in case of 2- and 2,5-diiodofurans by considering the relative intensities of their He I/He II spectra.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400844
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  • 121
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    Comparative Ab Initio study of electronic and ionic properties of lithium nitride (Li3N), lithium phosphide (Li3P), and lithium arsenide (Li3As) (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 461-478 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio Hartree-Fock band structure calculations are presented for the first time for lithium phosphide (Li3P) and lithium arsenide (Li3As) in the hexagonal P6/mmm crystal structure. Results are compared to those for lithium nitride (Li3N). The new calculations for Li3N agree with previous Hartree-Fock calculations, except for the valence band structure where results of previous pseudopotential calculations are confirmed. Geometry optimization for Li3P yields a lattice parameter a of 4.45 Å and a c value of 4.80 Å. These values differ markedly from experimental results reported to be 4.271 and 7.590 Å, respectively. A similar discrepancy is found for lithium arsenide: a = 4.60 Å and c = 4.96 Å have to be compared to the reported experimental values of 4.397 Å for a and 7.824 Å for c. Force constants are derived for in-plane and interplane vibrations. The band structures for Li3P and Li3As are found to be very similar to the one calculated for Li3N. Using Li3P as an example, it is shown how the band structure of the insulator can be derived from the band structures of the two metallic constitutent Li2P and Li monolayers. The metal-insulator transition occurs if the inter-plane distance falls below 4.25 Å. Contrary to expectations raised earlier, it is found that the 3d electrons in arsenic are strongly localized, evidenced by a very narrow d band width of 0.1 eV. They cannot be used to explain the difference in conductivity between the phosphide and the arsenide. A Mulliken population analysis gives charge distributions close to the ideal ionic structure (Li+)3X3-, X = N, P, and As. Overall it is found that hexagonal lithium phosphide and lithium arsenide arsenide are more similar to lithium nitride and less anisotropic than suggested previously. This discrepancy could be due to the use of polycrystalline samples in earlier experiments.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400843
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    1,5-C2B3H5 and C5H8, 1,5-C2B3H3 and C5H6: Carborane-hydrocarbon structural analogs with unusual three-center bondsDedicated to William Nunn Lipscomb in honor of his many important contributions to structural and theoretical chemistry. (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 489-505 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic structure of the polyhedral carboranes 1,5-dicarba-closo-pentaborane(5) and 1,5-dicarba-closo-pentaborane(3) is studied using ab initio calculations, and compared to that of their hydrocarbon analogs bicyclo[1.1.1]pentane and [1.1.1]propellane, respectively. The high symmetry and common topology of the carborane-hydrocarbon structural analogs force similar bonding patterns, and the carboranes show a unique three-center, two-electron CBC bond not previously observed in these species. This three-center bond is formally analogous to the σ-bridged-π bond in the hydrocarbons, but its strength is low and its C—C bond long. Analysis of the bonding in these carboranes along with that in 1,3-diborabicyclo[1.1.1]pentane, another[1.1.1]propellane analog, shows that the strength of their three-center bonds is directly related to the nature of the bridging group, but is independent of the type of bridgehead atom. 1,3-Diboretene, the carborane analog of bicyclo[1.1.0]butane, is also found to exhibit a similar bonding pattern to its hydrocarbon analog and to possess a CBC bond.
    Additional Material: 13 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400845
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    Preliminary theoretical study of acrylonitrile and its methyl derivatives as monomers for cathodic electropolymerization (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 507-526 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio calculations of the molecular geometry and electronic structure properties (charges, dipole moment, polarizability, HOMO and LUMO energies) of acrylonitrile, CH2=CH—C≡N, cis- and trans-2-butenenitrile, CH3—CH=CH—C≡N, 3-butenenitrile, CH2=CH—CH2—C≡N, and 2-methyl-2-propenenitrile, CH2=C(CH3)—C≡N are obtained at the 3-21G level. Results on three anionic derivatives of these molecules obtained at the 3-21+G level are also reported. Properties of the molecules in their isolated states are considered as a preliminary basis to compare initial steps of bulk and surface polymerization of vinylic monomers by electrochemistry under cathodic polarization.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400846
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    Solvation effects on the structure and reactivity of clusters (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 527-544 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Elucidating, from a molecular point of view, the differences and similarities in the properties and reactivity of matter in the gaseous compared to the condensed state is a subject of considerable current interest. Although there are a number of promising approaches to this problem, one of the alternatives involves the use of clusters that enable detailed spectroscopy and reactivity investigations to be accomplished as a function of degree of solvation under well controlled conditions. New insight into a variety of phenomena of interest in liquids have been derived from recent studies in our laboratory. In particular, the findings have contributed to unraveling the reactions of ionized functional groups in organic molecules that are influenced by solvation effects, identifying the structure of protonated complexes among species of varying proton affinities, and quantifying the variations in spectroscopic properties of chromophores as influenced by solvation and aggregation. Various examples from the author's laboratory are discussed, including solvation-driven reactions as well as alcohol and acetone dehydration reactions, the influence of clustering on the reaction of OH- with CO2, structures of protonated species comprised of water, ammonia, and trimethylamine; also presented are the results of studies of the influence of solvation on the absorption of photons in the chromophore of tyrosine, namely phenol.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400847
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    Calculations on the electronic structure and spectroscopy of C60 and C70 cage structures (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 557-568 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A study of the electronic structure and spectroscopy of models of C60 and C70 cage structures has been carried out using the intermediate neglect of differential overlap (INDO) model Hamiltonian. The geometry for these cages was obtained using gradient-driven methods, and at least in the case of C60, where information is available, is in good accord with the calculations of others. Using a small active space of only single excitations, both configuration interaction (CI) and random phase approximations (RPA) yield spectra in excellent agreement with that obtained from recent experiments. The oscillator strength of the band calculated at ∼47000 cm-1, however, dramatically diminishes as the active space is increased, even though the sum rule increases. We discuss this interesting observation as well as the calculated structure and spectrum of C70.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400849
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    An INDO/S-CI treatment including spin-orbit interaction based on Rumer spin functions. Application to the hydrated cerium ion (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 545-555 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We examine the inclusion of spin-orbit effects within the Rumer configuration interaction technique and discuss its implementation in the spectroscopic version of the intermediate neglect of differential overlap model (INDO/S-CI). An efficient strategy for calculating excitation energies, transition moments, and Mulliken populations for Rumer-adapted functions is described. As an example, results are presented for the ground and excited states of the hydrated trivalent cerium ion [Ce(H2O)9]3+, which confirm the low energy assignments to 4ƒ → 5 d transitions split by some 10000 cm-1 through spin-orbit coupling and ligand field interaction. Comparisons are made between this technique and one that we have used previously that utilizes configuration interaction over double-group adapted linear combinations of determinants.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400848
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    Electron-Atom interaction potential by DCS minimization (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 569-576 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The angular and energy dependence of minima of the differential scattering cross section (DCS) for electrons scattered elastically by selected target atoms is studied using the nonrelativistic Hartree-Fock wavefunction for the static field and local energy-dependent function for the exchange and polarization potentials for the target atoms. The parameters contained in the polarization potential are varied to determine the minima of the DCS with respect to the scattering angle and incident energy with the constraint that the integral cross section agrees with the experimental value within the uncertainty of 5% at a selected energy. The resulting effective interaction potential is then used to compute the DCS over the intermediate energy range for the target atoms. The computed values are in good agreement with recently published experimental and theoretical cross section for helium and neon atoms.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400850
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    A theoretical study of the photochemistry of methylcopper hydride: II. Formation and stability of the HCuCH3 intermediate complex (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 577-585 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using computational SCF and MCSCF followed by extensive variational and perturbational CI calculations, we study the insertion routes of a copper atom into the carbon-hydrogen bond of a methane molecule. Here we show the importance of the initial reaction routes of the interaction for obtaining the final products of maximal probability. Because of the initial conditions of this reaction, our study shows that not all of the HCuCH3 intermediate complex dissociation channels in Part I can be easily reached. Another important result presented is the nonlinearity of the intermediate product HCuCH3. Finally, the results are discussed in light of low temperature matrix photoexcitation experiments and a comparison of this Cu—CH4 interaction with previous studies of the activation of the hydrogen molecule by copper is presented.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400851
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    The charge distribution and the electric field gradient at the nuclei of two-coordinated N atoms (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 587-591 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: From ab initio SCF-MO calculation using a 6 - 31G** basis set, the relationship between the topology of the charge distribution and the electric field gradient (EFG) at the nuclei of the two-coordinated N atoms was determined in imines with R = H2C =, HFC =, NCHC =, and H3CHC =; di-imides with R = H, F, and CN; and the monocyclic azines with one and two N atoms in it. It was found that the N nuclear quadrupole coupling constant was determined by the nonbonded concentration of N valence shell while the asymmetry parameter has contributions from this shell and also from the rest of the molecule.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400852
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    Intermolecular vibrational resonance coupling: Intensity borrowing in polarized Raman spectroscopy (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 593-602 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of solvent-solute interactions on polarized and depolarized Raman intensity are investigated using perturbation theory, accounting for correlations in the relative orientations of the interacting transition dipoles. Two mechanisms for intensity borrowing are considered: interaction of the vibrational transition moments in the ground electronic states, and coupling of the electronic transition moments responsible for resonance Raman enhancement. The first type of interaction is shown to lead to measurable frequency shifts and depolarization ratio changes for two coupled vibrations which are infrared active and close in frequency. The second mechanism, not dependent on vibrational resonance, leads to perturbations of the depolarization ratio in resonance Raman, but not to vibrational frequency shifts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400853
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    An Ab Initio computational scheme for polymeric chains with fully converged coulomb and exchange lattice sums (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 603-618 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The restricted Hartree-Fock formalism applied to quasi one-dimensional translational systems embodies slowly convergent Coulomb and exchange lattice summations. In this contribution, an algorithm based on a Filon like quadrature procedure to carry out the k-space integration of density matrix elements is analyzed and its efficiency is illustrated by its application to the linear chains of hydrogen molecules. It allows the computation of Coulomb and exchange lattice sums to their asymptotic limit, and renders obsolete the empirical procedure of guessing the number of interactions to be included in the calculations.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400854
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    The Ab-Initio hybrid crystal orbital/molecular cluster approach to study the electronic structure of molecular crystals and reactions in the solid environment (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 619-628 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hybrid method having features of ab-initio crystal orbital and ab-initio molecular cluster methods is proposed. In the approach presented the molecular crystal is treated as an infinite chain in a direction z, while two other directions are simulated by finite interactions of the molecular type. The new approach is especially useful for an investigation of anisotropic crystals. Test calculations for the carbon dioxide crystal are presented. The method was also employed for the investigation of a dissociation pathway of C—N bond in nitromethane in nitromethane crystal.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400855
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    Theoretical properties of a 3-layer film of LiBeH3 (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 629-639 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The linear combinations of Gaussian-type orbitals-fitting function (LCGTO-FF) technique has been used to calculate the binding energy and electronic band structure of a 3-atom-thick film extracted from bulk LiBeH3 in the cubic perovskite structure. The film is composed of an interior layer of LiH sandwiched between two exterior layers of BeH2, i.e., there are eight atoms per unit cell (1 Li, 2 Be, and 5 H). The calculated cubic lattice parameter for the 3-layer (a = 5.74 au) lies roughly midway between the previously published theoretical lattice parameters for a BeH2 monolayer (5.51 au) and bulk LiBeH3 in the cubic perovskite structure (5.89 au). The 3-layer film is predicted to be a semimetal (i.e., zero-gap semiconductor), unlike both bulk LiBeH3 which is predicted to be a semiconductor, and monolayer BeH2, which is predicted to be a good metal. The metallic nature of the 3-layer is due to a Be surface state that cuts across the other valence bands of the film, in good agreement with an earlier prediction that cubic perovskite LiBeH3 cleaved to expose a BeH2 layer would provide a metallic surface on an insulating substrate. The fact that the density of states goes to zero at the Fermi level is a direct result of the symmetries of the one-electron states.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400856
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    Dissociative adsorption and associative desorption of H2 on a flat surface (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 641-657 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A quantum mechanical time-dependent method was used to study the dynamics of dissociative adsorption and associative desorption of H2 on a flat, static surface. We used a two-dimensional model in which the molecular axis was held parallel to the surface and the diatom internuclear separation and distance above the surface were the dynamic variables. A modified London-Eyring-Polanyi-Sato (LEPS) potential described the molecule-surface interactions. The wave function for the molecule was represented by its values on a spatial grid of points. The wave function was propagated by expanding the time evolution operator in a series of Chebyshev polynomials and using the properties of the Fourier transform to calculate the kinetic energy. The computational requirements of the problem were significantly reduced by using an L-shaped grid which deletes a large number of points where it is known a priori that the wave-function amplitude vanishes. State-to-state transition probabilities were calculated as a function of the initial translational and vibrational energy for potentials with early, late, and intermediate barriers. The location of the barrier has a strong effect on the energy threshold for reaction and on the distribution of energy between vibration and translation in the products.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400857
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    Theoretical study on Al multiple substitutions in the MFI zeolite (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 659-669 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this work we deal with ab initio and semiempirical calculations of single and multiple Al → Si replacements in the ZSM-5 structure. Substitutional energies for single replacements were obtained for cluster models of monomers, hexamers, and for the secondary building unit (SBU) of the zeolite by means of nonempirical SCF calculations, as well as the modified neglect of differential overlap (MNDO) method for extended clusters. The choice of the semiempirical methods for the study of multiple Si replacements by Al in the extended cluster model of the SBU is justified from the results with monomers and hexamers where the replacement energies obtained with MNDO are qualitatively the same as those from ab initio calculations. According to the results, a site occupancy order in the unit cell of the ZSM-5 network is derived from multiple Al → Si substitutions in the SBU, providing a theoretical basis for the Loewenstein-Dempsey Al sitting avoidance rules. Likewise, a Si/Al limit ratio in the Mobil FIve (MFI) zeolite, along with the corresponding Al distribution pattern in the unit cell, are also obtained.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400858
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    Nonadiabatic calculations for tdμ relevant for muon catalyzed fusion (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 671-686 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Due to the mass effect, muonic molecular ions are about 200 times smaller than their electronic counterparts. The proximity of the nuclei in the tdμ ion results in fusion taking place within a picosecond. The properties of this ion are central to understanding the phenomenon of muon catalysis. We developed a computational method of solving the nonadiabatic Schrödinger equation for the bound and resonant states of tdμ and its isotopic analogues. The method takes into account both the Coulomb interactions and the strong nuclear forces responsible for the fusion reaction. The wave functions obtained from our method were used to predict very accurately branching ratios and transition rates relevant for various stages of the muon catalytic cycle. Knowledge of these quantities will guide the experiments and help to answer the question of feasibility of net energy production via muon catalysis.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400859
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    Computation of scanning tunneling microscope images (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 687-702 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This article describes the computation of the tunnel current in a scanning tunneling microscope (STM). The calculation accounts for the three-dimensional scattering taking place simultaneously in the first atomic layers of the sample and in the apex of the probing tip. The model is built with the following ingredients: (a) the tip is represented by a cluster of atoms attached to an otherwise planar, free-electron metal surface, and (b) the analyzed sample is a planar free-electron metal with a local potential corrugation induced by an isolated molecule or adatom. The potential barrier includes the strong bending effect due to the image-charge formation occurring as the tunneling electron crosses the gap between the tip and the sample. The specific theoretical approach designed to solve this scattering problem exploits the fast Fourier transform algorithm to construct a transfer matrix in a mixed real- and momentum-spaces representation. The total current is obtained by summing the contributions of all scattered waves traveling in the barrier between the tip and the sample, and it is studied in this article for various positions of the tip relative to the adsorbed atomic cluster. The theory is used here to simulate the scan of a model-aluminum atom on a free-electron metal substrate using electrons focused by a single-atom tungsten tip.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400860
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    Bonding in heteronuclear transition-metal diatomics: NbIr (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 689-698 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bonding in transition-metal molecules presents novel features: (i) s electron bonding is overcome by multiple d electron bonding, (ii) intraatomic exchange favoring atomic magnetization competes with bonding that tends to pair the electrons, and (iii) in the heteronuclear dimers, the ionic terms may be important due to strong charge-transfer effects. The NbIr heteronuclear diatomic molecule shows all these features clearly. The cellular multiple scattering-xαβ calculation presented in this paper shows the ground state to correspond to antiferromagnetic coupling between the highly magnetic Nb atom and the Ir atom. A one-electron charge transfer from Nb to Ir was found; the result is an ionic structure, Nb+Ir-, for the dimer. The computed equilibrium distance, 4.100 a.u., corresponds to a region where d bonding strongly overcomes the s bonding, which alone would have stabilized the molecule at 5.950 a.u. At intermediate interatomic separations, 5.35 a.u., the NbIr system has a state in which all molecular orbitals are bonding with a high hybridization between the ns and (n - 1)d electrons of each atom, resulting in a (almost entirely) covalent high multiple-bond formation for this meta-stable state of the dimer.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560390506
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    Construction of orthogonal subspaces (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 747-754 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An orthogonalization procedure is presented that allows construction of at least (n-m) vectors orthogonal to {Xj}, j equals; 1, m, by linear combinations solely among {ηi}, i equals; 1, n, n〉m, and 〈Xj/ηi〉≠0. An important application of the procedure is in effective core potential methods for which valence orbitals can be constructed that are orthogonal to the core orbitals and yet involve no component of the core. Thus, a separate calculation for only the valence electrons can be performed without any explicit reference to the core electrons (orbitals).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390510
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    Quasi-particle equation from the configuration-interaction (CI) wave-function method (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 225-242 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Green-function method is a well-known way to reduce the quantum mechanical problem of n electrons moving in the field of clamped nuclei to the problem of solving a one-electron Schrödinger equation (the quasi-particle equation) involving a pseudopotential (the self-energy). This method is widely used in solid-state, low-energy electron-molecule scattering, ionization, and electron attachment theory, and much work has focused on finding accurate self-energy approximations. Unfortunately, the operator nature of the fundamental quantity (Green function) in the usual quasi-particle equation formalism significantly complicates the derivation of self-energy approximations, in turn significantly complicating applications to inelastic scattering and multiconfigurational bound-state problems. For these problems or wherever the operator approach becomes inconvenient, we propose an alternative quasi-particle equation derived wholely within a configuration interaction wave-function formalism and intended to describe the same phenomenology as does the Green function quasi-particle equation. Our derivation refers specifically to electron removal but is readily generalized to electron attachment and scattering. Although the Green function and wave-function quasi-particle equations are different, we emphasize the parallels by rederiving both equations within the equations-of-motion formalism and then producing a wave-function analog of the Green function two-particle-hole Tamm-Dancoff approximation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400206
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    1991 Sanibel symposia list of participants (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. ix 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400704
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  • 142
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    Effect of proton transfer on neighboring hydrogen-bond strength (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 37-48 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transfer of a proton from A to B in AH+‥B‥C to form A‥+HB‥C is expected to enhance the binding energy of C to the remainder of the H-bonded chain since C is now adjacent to a charged ion rather than to a neutral molecule. But since the actual proton motion between A and B is typically only 1 Å or so, the interaction should be considerably less than that in isolated +HB‥C. Ab initio calculations with a variety of basis sets are used to quantitatively measure the enhancement of this binding energy. Systems investigated include the homotrimers of water and of ammonia, ammonium-formate-water, and formic acid-imidazole-water.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400709
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  • 143
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    Biographical sketch of Michael KashaInstitute of Molecular Biophysics and Department of Chemistry, Florida State University, Tallahassee, Florida 32306-3015 (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 235-250 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390304
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  • 144
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    Solvent effects in dense gases (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 399-409 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of perturber gases, partial pressures in the range 0-50 atm, on the absorption spectra of high-n Rydbergs, n ≥ 10, in methyl iodide and benzene have been investigated. The perturbers were rare gases and H2. It has been shown that the spectroscopic energy shift Δ = Δ(ρ, n) is given by Δ = Δ°ρ, where ρ is the number density of the perturber, for n ≥ 10. The shift data can be interpreted using a Fermi model, and values of scattering lengths for perturbers can be extracted. These scattering lengths are internally consistent, independent of the absorber, and in excellent agreement with electron-swarm results. Given that the Fermi model is nonspecific and microscopic, scattering shifts and lengths for mixtures of perturber gases can be predicted. These predictions, having been verified by experiment for He/Ar mixtures, provide a means of “tailoring” any required scattering length. Finally, it is shown empirically that the determinative scattering parameter is the polarizability of the perturber, and a universal relationship a = -0.26α + 1.18 between scattering length a, in Bohr radii, and polarizability α is found to exist.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390316
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  • 145
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    The intermolecular vibrations of the bifurcated water dimer: An Ab initio study (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 449-454 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The intermolecular modes of the bifurcated water dimer are determined at the HF level using an extended basis set. In these computations, the donor libration frequency is found to be real and the bifurcated structure does not collapse toward the linear dimer. This result is contrary to all previous ab initio computations, which have predicted a Hessian with one negative eigenvalue. A good representation of other intermolecular modes, such as the libration of the acceptor, also requires an extended basis set. An interesting infrared active transition is predicted around 444 cm-1. This transition, which corresponds to the donor wag, is found in the low-temperature spectrum of water in a N2 matrix.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390320
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  • 146
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    Masthead (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390401
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  • 147
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    String model for the rate constant of nonadiabatic solvation in the hydration reaction of carbon dioxide (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 561-583 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Perturbation theory for the rate constant of nonadiabatic solvation is presented. Miller's treatment of the RRKM theory is used for the unperturbed rate constant, and thereby the “string model” of chemical reaction is used for the description of the perturbation of solvation. The reaction path under the influence of the external force field is defined as the intrinsic reaction coordinate (IRC) that is treated as a string. The string is thrown in the external static force field that acts as a nonadiabatic source of perturbation. As an application of the present treatment, the effect of the external point charge for hydration reaction of CO2 is calculated as a preliminary model for catalytic activity of the carbonic anhydrase in the tissues and lung capillary vessels.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390404
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  • 148
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    Approximate noninteracting kinetic energy functionals from a nonuniform scaling requirement (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 379-388 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have recently proven an inequality for the exact noninteracting kinetic energy density functional \documentclass{article}\pagestyle{empty}\begin{document}$ T_s [n]:\mathop {\lim }\limits_{x \to \infty } T_s [n_\lambda ^x] \le T_s [n_s^y [n] + T_S^2 [n] 〈 \infty,where{\rm }n_\lambda ^x (x,{\rm }y,{\rm }z) = \lambda n(\lambda x,{\rm }\lambda {\rm y, }\lambda z) $\end{document}. It is known that the gradient expansion through fourth order, TsGE[n], violates this inequality. Toward improving TsGE[n], we have constructed two new functionals, Ts1[n] and Ts2[n], by keeping the zeroth and second orders in TsGE[n] and replacing the fourth order with two simple terms, respectively, so that these new functionals satisfy the inequality. Numerical tests are presented for Ts1[n], Ts2[n], and TsGE[n] and for the gradient expansion through second order. Hartree-Fock and hydrogenic atomic densities are employed.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400309
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  • 149
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    Erratum: Dirac-Fock self-consistent field method for closed-shell molecules with kinetic balance and finite nuclear size (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 429-432 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400315
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  • 150
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    Masthead (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400401
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  • 151
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    A quantum chemical investigation of pyrolysis reactions of glyoxylic acid ethylester (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 491-500 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two possible reaction paths for the pyrolysis of the ethylester of glyoxylic acid have been studied by ab initio molecular orbital calculations. The basis sets 3-21G and 6-31G* have been used, and electron correlation has been included by Møller-Plesset calculations up to fourth order. Our calculations indicate that the reaction leading to acid and ethylene through a 6-membered ring transition state is favored relative to a process involving a formyl hydrogen transfer via a 5-membered ring to the alkyl unit leading to ethane, CO, and CO2. The predicted activation energies for these two reactions obtained at the highest level of calculation, MP4(SDTQ)/6-31G*, are 50.4 and 71.7 kcal/mol, respectively. The transition states have RHF wave functions that are stable relative to UHF solutions using the 3-21G basis. The geometry of the transition states and IRC following indicate that both reactions are strongly asynchronous: The C—O bond rupture is virtually completed before hydrogen transfer occurs. For comparative purposes, analogous calculations have been performed for the ethylester of formic acid, where it is confirmed that a 6-membered ring transition state is preferred relative to a 4-membered one by around 42 kcal/mol at the highest level of calculation.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400405
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  • 152
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    A time-dependent molecular orbital approach to electron transfer in ion-metal surface collisions (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 545-558 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A time-dependent molecular orbital method has been developed to study charge transfer in collisions of ions with metal surfaces at energies between 1 and 100 au. A set of localized basis functions consisting of generalized Wannier functions for the surface and s- and p-atomic functions for the ion, is used to separate the system into primary and secondary regions. An effective Hamiltonian and time-dependent equations for the electron density matrix are obtained in the primary region, where most charge transfer occurs. The equations for the electron density matrix are solved with a linearization scheme. The method is suitable to study atomic orbital orientation for collisions of ions and surfaces. A model calculation for Na+ + W(110) collisions with a prescribed trajectory is presented. The interaction potentials between the W(110) surface and Na+ 3s and 3p orbitals are calculated from Na+ pseudopotentials. Results show that the yield of neutralized atoms in 3p states changes as the collision energy is lowered.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400409
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  • 153
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    On the conditions for physical admissibility of Schrödinger wave functions (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 605-609 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that the dispute about the conditions for physical admissibility of Schrödinger wave functions may be settled if the following two questions are clarified: (a) Are these condittions rooted in the foundations of quantum mechanics or invoked only for particular physical models? (b) Do we consider either the position-space wave function or the momentum-space wave function? Both the case of closed states and scattering states are considered. Some general remarks about these conditions are made in the Conclusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400504
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  • 154
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    Macromolecular dynamics on a shared-memory multiprocessor (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 175-179 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: This is a study of the effect of data structures and algorithms on parallelism and vectorization for the molecular dynamics package GROMOS. About 80% of the computing time (for the GROMOS benchmark) is spent on the nonbonded interactions, and an important issue is the method that is used for finding all pairs of atoms (actually atom groups) which are within a given cutoff radius of each other. Favored by the authors of GROMOS is the use of the (Verlet) neighbor list with direct calculation of all distances. Substantial restructuring of their code for the nonbonded interactions has resulted in a speedup of a factor 6.9 for the eight-processor Alliant FX/8 through the use of concurrent subroutine calls. Vectorization gave a further improvement of 30%. However, the direct calculation of all distances does not scale up linearly with the number of atoms. (Nor would neighbor lists be needed if cutoffs were abandoned in favor of such techniques as the fast multipole method). Therefore an alternative GROMOS subroutine that implements the “gridcell plus linked list” approach without a neighbor list was also rewritten and tested. This resulted in the discovery of an apparent flaw in an early study of the relative merits of the two algorithms. It is observed that actually the neighbor list version of GROMOS is not much faster.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120206
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    A comparison of conformational energies calculated by molecular mechanics (MM2(85), Sybyl 5.1, Sybyl 5.21, and ChemX) and semiempirical (AM1 and PM3) methods (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 200-208 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Conformational energies of different conformers have been calculated for a series of molecules using various molecular mechanics and semiempirical methods. The quality of the force fields has also been tested by calculating barriers to rotation about carbon-carbon bonds. The molecular mechanics force fields used are MM2(85), Sybyl 5.1, Sybyl 5.21, and ChemX, ver. Jan 89. The semiempirical methods used are AM1 and PM3. Molecules with different functional groups, for which good experimental data exist, have been selected. The semiempirical methods generally calculate barriers to rotation which are lower than the experimentally determined. The conformational energies for hydrocarbons are reasonably well reproduced by all tested methods although MM2(85) gives the quantitatively best agreement with experiments. For compounds containing oxygen, nitrogen and halogens MM2(85) gives results which are in best agreement with the experimentally determined values.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120209
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  • 156
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    Minimization and molecular dynamics studies of guanosine and Z-DNA modified by N-2-acetylaminofluorene (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 147-166 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The modeling program AMBER 3.0 was used to study the conformations adopted by the C8-substituted guanosine adduct of the carcinogen N-2-acetylaminofluorene (AAF), called dGuo-AAF. This conformational study was extended to the hexamer d(CGCGCG)2 in the Z form, modified by AAF at guanine G4 with the carcinogen situated at the helix exterior in two different orientations (named ZAAF-5′ and ZAAF-3′). Considering the importance of electrostatic interactions in case of charged molecules like nucleic acids, minimization and molecular dynamics (MD) were performed using different electrostatic parameters (dielectric functions and scale factors). For that purpose, a subroutine allowing the use of a sigmoidal distance-dependent dielectric function εcal has been added to the program. For dGuo-AAF, the results show a great importance of the starting conformation and of the force field parameters on the minimization and MD behaviors. For the AAF-modified Z-DNA, the results display a pronouned dependence on the choice of the set of electrostatic parameters as well. With the distance-dependent dielectric function ε = r, the force field parameters favor the formation of intramolecular H bonds, which can lead to important distortions of Z-DNA. The use of ε = 4r or ε = εcal attenuates effectively such a tendency, except in full MD simulations. The dielectric function εcal is computing intense, but often similar results are obtained with ε = 4r, especially with the use of the BELLY option. AAF appears to prefer the ZAAF-5′ conformation, i.e., with the fluorene ring stacking on the sugar phosphate backbone of the following 5′ C-G bases. Such a conformation is further stabilized by an intramolecular hydrogen bond between the amino group of the 3′ cytosine and the carbonyl group of AAF. The fluorene ring, although mobile around its long axis, does not flip-flop between its two main orientations, ZAAF-5′ and ZAAF-3′. The presence of the AAF does not prevent the ZI to ZII transitions. Whatever the electrostatic parameters, the presence or absence of AAF, the cytosine sugars stay in the C2′-endo pucker domain. In unmodified Z-DNA, the guanine sugars stay in the C3′-endo region, except for the terminal guanines which transit to the C2′endo region. In modified Z-DNA, the sugar of the modified guanine behaves as a terminal guanine sugar.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120203
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  • 157
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    MRD-CI potential surfaces using balanced basis sets. VI. Correlation of bond order with bond function composition for first-row diatomic molecules (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 690-696 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: This article presents theoretical calculations on bond energies for the first-row diatomics C2, CN, CO, CF, N2, NO, NF, O2, FO, and F2, which vary in bond order from one to three. The atomic-centered basis functions are systematically augmented with bond functions (BFs), which range in composition from (sp) to 2(spd), to determine the basis set which yields a dissociation energy closest to the experimental De. A strong correlation is found to exist between the bond order and the number of BFs required in the optimum basis set. Based on these results, we are able to predict the optimum composition of the BF basis which should be added to a DZP-quality AO basis set for a case in which only the bond order is known. These optimized BF basis sets are shown in the accompanying article to give more accurate potential curves than larger basis sets without bond functions.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120606
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    The use of ultraviolet resonance Raman intensities to test proposed molecular force fields for nucleic acid bases (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 731-741 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The harmonic molecular force fields for the nucleic acid bases, cytosine, and guanine, that have been previously published by several investigators are tested by the calculation of the relative intensities of the in-plane modes in the ultraviolet resonance Raman (UVRR) effect from the two lowest lying absorption bands using a theoretical approach devised previously.1-3 Since only a fraction of the 2N - 3 in-plane vibrations of a molecule are active in the UVRR, the two criteria that are taken for the adjustment of the force constant are: (1) the closest possible agreement between the observed and calculated frequencies of the 2N - 3 in-plane vibrations, and (2) the closest possible agreement between the calculated and observed intensities of those few vibrations that are strongly active in the ultraviolet resonance Raman effect. In particular it is necessary that the force constants be adjusted to avoid the calculation of intense Raman lines with frequencies that are not observed in the UVRR spectrum. Using this criteria, a new force field has been developed that appears to give better agreement with the observed UVRR intensities than previously published ones. It is suggested that this calculation of the UVRR intensities can be used to refine molecular force fields in combination with other methods such as isotopic replacement currently in use to refine force constants.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120610
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  • 159
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    Conformational energies and rotational barriers in 3-methyl-1-butene and 1-butene: An ab initio and molecular mechanics study (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 839-843 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The calculated result obtained with MM2(87) for the rotation of the isopropyl group in 3-methyl-1-butene is not in agreement with experimental data. In order to reparametrize the Csp2-Csp3-Csp-Csp3 torsional angle, 3-methyl-1-butene and 1-butene have been studied by molecular mechanics (MM2(87)) and ab initio (MP2/6-31G* and MP3/6-31G*) calculations. The reparametrization of the torsional angle gives calculated results from MM2(87) in agreement with experimental data and ab initio calculations for both 3-methyl-1-butene and 1-butene. The calculated barriers for the rotation of alkyl groups in alkylbenzenes are improved with these new parameters.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120708
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  • 160
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    Conformational studies of 2-methylbutyronitrile and 3-methyl-1-pentyne by vibrational spectroscopy and molecular mechanics (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 880-884 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Vibrational spectra were obtained for the structurally similar compounds 2-methylbutyronitrile and 3-methyl-1-pentyne, and vibrational assignments were made with the aid of normal coordinate calculations. Molecular mechanics calculations were also made, and each compound was shown to exist as a mixture of three conformers, with the most stable conformer being the one with the two methyl groups trans to each other. Results of the calculations are given.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120714
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    Dielectric boundary smoothing in finite difference solutions of the poisson equation: An approach to improve accuracy and convergence (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 909-912 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Finite difference methods are becoming very popular for calculating electrostatic fields around molecules. Due to the large amount of computer memory required, grid spacings cannot be made extremely small in relation to the size of the van der Waals radii of the atoms. As a result, the calculations make a rather crude approximation to the molecular surface by defining grid line midpoints discontinuously as either interior or exterior. We present a method which “smoothes” the boundary, but more accurately models the potential from the analytic solution of the discontinuous dielectric problem and improves convergence in electrostatic energy calculations. In addition, a small improvement in convergence rate is observed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120718
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  • 162
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    A vectorized algorithm for calculating the accessible surface area of macromolecules (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 868-871 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: An algorithm is presented for calculating the solvent accessible surface area of proteins using a three-dimensional grid. Since it requires only calculations based on single atomic positions, the algorithm is easy to be vectorized. It has been implemented on ST100 and may also be implemented on supercomputers like the CRAY or the CYBER. Results on several proteins indicate that its deviation from that of the Shrake-Rupley algorithm is very small while the computation time is much reduced.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120712
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    Principal component analysis of dipole moment derivative signs of chloroform (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 885-890 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The use of principal components as a basis for a graphical procedure to analyze polar tensor data is proposed. Molecular orbital and experimental polar tensor data for all possible sign combinations of the ∂p/∂Qj of CHCl3 and CDCl3 are represented graphically as principal component scores facilitating sign selection for the ∂p/∂Qj. The graphs are particularly useful in analyzing an apparent conflict in ∂p/∂Qj sign choices based on the isotopic invariance criterion and molecular orbital results for the A1 symmetry species of these molecules. The numerical impacts of individual sign ambiguities for the ∂p/∂Qj on the polar tensor data are measured by the variances associated with the principal components. Assuming the ∂p/∂Qj sign sets with indeterminate signs provide replicated results for the polar tensor elements, their errors are estimated and compared with errors obtained previously by propagating intensity uncertainties through the polar tensor equations.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120715
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  • 164
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    Charges derived from distributed multipole series (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 913-917 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A novel method to calculate electrostatic charges is proposed. Partial charges are fitted to reproduce the electrostatic potential of a distributed multipole series without explicitly evaluating electrostatic potentials. The calculation is economical and results in charges reflecting the symmetry properties of charge centers and being independent of molecular orientation.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120802
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  • 165
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    Molecular geometries and heats of formation of C60 and C70 as computed by MM2-87 (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 1129-1133 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: MM2-87 calculations have been performed on C60 (buckminsterfullerence; footballene) and C70 with full energy minimization. The steric energies for C60 and C70 were computed to be 179.9 and 177.9 kcal/mol, respectively. The heats of formation for C60 is found to be more stable than C60. The two bond lengths for C60 were computed to be 1.393 and 1.444 Å. Eight different bond lengths were found for C70 ranging from 1.386 to 1.452 Å. Bond angles, dihedral angles, and moments of inertia are also reported for the compounds.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120911
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  • 166
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    Efficient search for all low energy conformations of polypeptides by Monte Carlo methods (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 1065-1076 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The Metropolis Monte Carlo method has been added to the program FANTOM for energy refinement of polypeptides and proteins using a Newton-Raphson minimizer in torsion angle space. With this extension, different strategies for global minimization of the semiempirical energy function ECEPP/2 by various temperature schedules and restriction of conformational space were tested for locating local minimum conformations with low energy of the pentapeptide Met-enkephalin. In total, 1881 conformations below -10 kcal/mol were found. These conformations could be represented by 77 nonidentical conformations which were analysed for their pattern of hydrogen bonds, types of tight turn, pairwise root-mean-square-deviation (rmsd), Zimmermann codes and side chain conformations. All low energy conformations below -10.4 kcal/mol show strong similarity to the global minimum conformation in the backbone structure.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120904
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  • 167
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    Masthead (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991) 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540121001
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  • 168
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    Toward accurate transferable electrostatic models for polypeptides: A distributed multipole study of blocked amino acid residue charge distributions (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 1187-1197 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We have developed a method for building up accurate electrostatic models for polypeptides, based on a distributed multipole representation of the SCF charge densities for the dipeptides (CH3.CO.NH.CHR.CO.NH.CH3) of the naturally occurring amino acids. It is based on the observation that each peptide residue has almost the correct formal charge (0, ±1). We find that the variations in the backbone charge distributions (excluding proline) with sidechain have a negligible effect on the predicted electrostatic potential around the residue. However changes in the atomic multipoles with the torsion angles (φ, ψ, χ) are more significant, and may need to be taken into account if electrostatic potential close to the residue is required to high accuracy. This type of DMA peptide library provides more accurate, more theoretically based, estimates of the electrostatic potential around polypeptides than current models.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540121005
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  • 169
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    Structural effects of fluorine substitution in proteins (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 180-185 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The consequences of substitution of fluorine for the para hydrogen of a phenylalanine residue in ribonuclease-S were investigated by conformational energy calculations using the AMBER force field. Both the fluorine-containing protein and the corresponding nonfluorinated material were subjected to conformational adjustment through energy minimization and the minimum energy structures so defined were compared. Fluorine substitution leads to small alterations in many atomic positions in the protein, with adjustments at at sites more than 0.5 nm from the fluorine appearing to be somewhat larger than those within the immediate vicinity of the fluorine. Several atoms proximate to the fluorine atom were observed to move toward the fluorine while others in the same vicinity move away. The greater bulk of the fluorine atom and the strongly different electronic properties of fluorine compared to hydrogen thus appear to be insufficient to cause a consistent, unidirectional change in nearest-neighbor interactions upon introduction of a fluorine atom into a protein structure. Virtually all changes in atomic positions that are predicted by these calculations would be barely detectable by a crystallographic study with a resolution of 0.2 nm.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120207
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  • 170
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    A complete shape characterization for molecular charge densities represented by Gaussian-type functions (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 220-230 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: An algorithm for a detailed 3-D characterization of the shapes of molecular charge distributions is implemented, tested and applied for a family of AB2 molecules. The characterization is performed by computing a number of topological invariants (“shape groups”) associated with a continuum of molecular surfaces: the complete family of all electronic isodensity contours for the given molecules. These shape groups (the homology groups of truncated surfaces derived from isodensity contours) depend continuously on two parameters: a density value defining the density contour, and a reference curvature value, to which the local curvatures of the isodensity contours are compared. The electronic charge distribution is modeled by means of Gaussian-type functions. The method employs an explicit form of the charge density function in order to compute the curvature properties for the molecular surfaces analytically, from which the shape groups are derived by the algorithm. No visual inspection is required for the characterization and comparison of shapes of molecular charge densities, as these are done algorithmically by the computer. However, visual inspection of the results of the shape analysis is a possible option. For a given molecule, in a given nuclear configuration, the technique provides a two-dimensional shape map, displaying the distribution of shape groups as a function of the local curvature and the level set value (the value of the charge density at the contour). The computer program GSHAPE performs the analysis of shape maps automatically. This feature makes it potentially useful in the context of computer-aided drug design, where unbiased, automated shape characterization methods are valuable tools. As examples, several two-dimensional shape maps for simple systems are discussed. The changes induced in these maps by a change in the nuclear geometry, as well as by the changes of the nuclear charge, are also analyzed. The method is applicable to large biomolecules of interest if charge density information is available.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120212
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  • 171
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    A simple approximation for the vibrational partition function of a hindered internal rotation (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 266-270 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A simple formula is presented for calculating the approximate partition function of a hindered internal rotational mode of a polyatomic molecule. The formula gives useful accuracy over the whole range from harmonic oscillator to hindered rotator to free rotator.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120217
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    Comparison of compuational methods for simulating nuclear Overhauser effects in NMR spectroscopy (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 292-300 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Various algorithms for solving the Solomon equations describing nuclear Overhauser effects (nOes) in NMR spectroscopy have been compared. The applicability of the eigenvalue/eigenvector and the numerical integration approaches have been investigated. The eigenvalue/eigenvector approach is not a computationally efficient means of simulating nOe experiments in which a saturating radiofrequency field is applied during the time course. For experiments in which nOes develop in the absence of an RF field, this approach should only be used in simulating a full NOESY spectrum. Integration schemes have been found to be more efficient at simulating nOe experiments in which the nOe evolves in the presence of a saturating field, at simulating a partial set of initial perturbation experiments and at simulating a few rows or columns in a NOESY spectrum. Various integration schemes were applied to a two-spin system for which an analytic solution is available and to a model B-DNA oligonucleotide hexamer. The previously unused Taylor series algorithm was found to be superior to the Euler, midpoint, and fourth-order Runge-Kutta methods with regard to integration accuracy/computation time. An adaptive step size control routine for the Taylor series integration scheme was developed. Integration schemes can be speeded up in a simple fashion by introducing a distance cutoff for the dipolar interaction. Using a cutoff of 8 Å the Taylor series algorithm was able to compute the NOESY spectrum more rapidly than the eigenvalue/eigenvector algorithm for large spin systems at short mixing times. At longer mixing times the eigenvalue/eigenvector approach becomes the more efficient scheme.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120303
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  • 173
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    Conformational dynamics of polypeptides and proteins in the dihedral angle space and in the cartesian coordinate space: Normal mode analysis of deca-alanine (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 359-368 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Effects of different treatments of the degrees of freedom of bond length stretching and bond angle bending in computational analysis of conformational dynamics of proteins and polypeptides are assessed. More specifically, the normal mode analysis of conformational dynamics of α-helix of deca-alanine has been carried out both in the dihedral angle space (DAS) and in the Cartesian coordinate space (CCS). Almost perfect one-to-one correspondence has been found between normal modes in the CCS with frequencies less than 128 cm-1 and those in the DAS with frequencies less than 164 cm-1. Patterns of atomic displacements in the corresponding modes are very similar. This indicates that the effects of fixing degrees of freedom of bond length stretching and bond angle bending on the very-low-frequency normal modes in the CCS with frequencies less than 128 cm-1 are almost solely to increase the frequencies by about 20%. The conclusion indicates that the different treatment of these degree does not lead to qualitatively different results as long as low-frequency motions are concerned. Based on the results of calculation, mechanical property of the α-helix of deca-alanine is discussed.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120309
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  • 174
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    Comparison of AM1 and ab initio calculation of the carbon-carbon bond rotation in ethylene glycol diacetate (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 742-745 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The C-C glycol bond rotational energy in ethylene diacetate as a polyester model was compared using the semiempirical method AM1 and an ab initio method with an STO-3G basis set. The results were qualitatively much different depending on the method used. Ab initio calculations showed the expected minima at 180 and near 60 (69.6) degrees dihedral angle with maxima at 0 and 120 degrees. The AM1 rotational curve indicated an apparent minimum at a 90 degree dihedral angle, a shallow, apparent maximum at 180 degrees and an apparent maximum at 0 degrees which could not be confirmed as minima or maxima via frequency calculations. Ethylene diacetate analog compounds with one or two ester oxygens replacing methylene group(s) gave curves with AM1 having the general shape for ethylene diacetate by the ab initio method, indicating a parameterization problem for the otherwise very useful AM1 to correctly handle a compound with only two carbons between the two electronegative oxygen atoms thus rendering this method currently unsuitable for examination of rotational energy barriers of such polyester model compounds.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120611
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    Masthead (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991) 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120801
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  • 176
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    Detection of cavities in a set of interpenetrating spheres (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 918-922 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A general topological procedure is described that is able to detect cavities of all shapes and sizes in a system of interpenetrating spheres. The procedure is coupled to an analytic algorithm for computing surface areas and volumes, but as such, involves only logical operations and is therefore not subject to numerical imprecision. Its application to the identification of internal cavities in molecular systems is illustrated.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120803
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    Variable atomic radii based on some approximate configurational invariance and transferability properties of the electron density (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 1198-1210 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The purpose of this study is to design a technique that generates a variable van der Waals-like surface for any desired charge density value of a molecule. The method is based on the recognition that for each fixed density value, within a wide range, certain shape features of the electron density contours are approximately invariant under configuration rearrangements, such as bending and stretchings in polyatomic molecules. These invariants appear in the form of spherical regions in space around the nuclei, where no density contours of a given level set value enter. These regions, the so-called invariant cores, behave as approximately transferable quasi-atomic spherical surfaces. We have evaluated these cores in molecules, and also approximated them in terms of the electron density of isolated atoms. The properties of these quasi-atomic surfaces allow one to design a scale of variable atomic radii based on the size of the transferable isodensity spheres. In this work we provide a detailed description of the dependence of the diameters of these spheres on the electron density values. We show that, by using this scale of radii, it is possible to design fused-sphere molecular models that closely mimic isodensity surfaces for a whole range of density values. The results discussed here allow one to relate molecular size with charge density. We propose the use of these scales for the construction of more realistic van der Waals model surfaces when studying molecular shape in the context of computer-assisted molecular modeling.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540121006
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  • 178
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    On the use of electrostatic potential derived charges in molecular mechanics force fields. The relative solvation free energy of cis- and trans-N-methyl-acetamide (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 1232-1236 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We have carried out free energy perturbation calculations on the relative solvation free energy of cis- and trans-N-methyl-acetamide (NMA). Experimentally, the solvation free energy difference has been found to be near zero. Using 6-31G* ab initio electrostatic potential derived charges for both the cis and trans conformations, we calculate a solvation free energy difference of 0.1 ± 0.1 kcal/mol. Using the 6-31G* charges derived for the trans conformation for both the cis and trans models leads to a solvation free energy difference of 0.9 ± 0.1 kcal/mol, compared to the value of 2.2 kcal/mol determined for the OPLS model for trans-NMA.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540121010
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  • 179
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    Vector and parallel algorithms for the molecular dynamics simulation of macromolecules on shared-memory computers (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 1270-1277 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A detailed description of vector/parallel algorithms for the molecular dynamics (MD) simulation of macromolecular systems on multiple processor, shared-memory computers is presented. The algorithms encompass three computationally intensive portions of typical MD programs: (1) the evaluation of the potential energies and forces, (2) the generation of the nonbonded neighbor list, and (3) the satisfaction of holonomic constraints. We implemented the algorithms into two standard programs; CHARMM and AMBER, and obtained near linear speedups on eight processors of a Cray Y-MP for cases (1) and (2). For case (3) the SHAKE method demonstrated a speedup of 6.0 on eight processors while the matrix inversion method demonstrated 6.4. For a system of water molecules the performance improvement over the standard scalar SHAKE subroutine in AMBER ranged from a factor of 165 to greater than 2000.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540121016
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    Maximum overlap symmetry orbitals (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 729-746 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Based on the principle of maximum overlap, a new simple method is suggested for constructing the symmetry orbitals of arbitrary molecules and the delocalized molecular orbitals of molecules that do not involve the rings with an odd number of atoms. All these orbitals, called “maximum overlap symmetry orbitals,” are determined by an extended maximum overlap criterion and form the bases for the irreducible representations of the molecular point symmetry group. The theoretical analysis and the numerical results show that the obtained molecular orbitals are close to those obtained from the customary LCAO method, and calculation by the proposed method requires less computing time than does the LCAO method, thus illustrating a fact that the method is not only a reasonable approximation of the LCAO method, but simpler and feasible in large molecular systems.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390509
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    A calculation of the isotropic and anisotropic spectral moments of the dipole oscillator strength distribution of N2 (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 755-766 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We calculate a range of isotropic and anisotropic spectral moments of the dipole oscillator strength distribution for N2 in the random phase approximation. The internuclear dependence of, in particular, S∥(k) is nonnegligible and vibrationally averaged moments are reported. The results are compared to other calculations and to experiment when available, and we conclude that the scheme gives reliable results. Based on our results, we predict a 10% anisotropy in the stopping power of oriented N2 molecules.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390602
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    Hydrogenlike atoms in uniformly charged sphere model of atomic nucleus. II. Application of basis-set expansion method (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 813-821 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The basis-set expansion method has been applied to the nonrelativistic and relativistic ground states of one-electron atoms H, Ar17+, Xe53+, Hg79+, and U91+ in the uniformly charged sphere (UCS) and the point-change (PC) models of atomic nucleus, using the Gaussian-type basis functions. The energies and the radial expectation values, especially 1/r2, converges faster in the UCS model than in the PC model. In the PC model, larger values of the exponent parameters of the basis functions are required both in the nonrelativistic and the relativistic calculations. Even in the UCS model, the larger values of the exponent parameters are needed in the relativistic calculations.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390606
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    Approximate density matrices and Husimi functions using the maximum entropy formulation with constraints (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 823-837 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The entropy of an electronic system is defined in terms of the Husimi function, a nonnegative distribution function in phase space. The Husimi function is calculated by maximizing the entropy subject to the constraints that the Husimi function give a Gaussian convolution of the desity when integrating over the momentum coordinates and that its second moment with respect to momentum give a sum of Gaussian convolutions of the density and the kinetic energy density. The result is compared with the Wigner function. Equations are given for calculating the density matrix from the Husimi function. The resulting equation for the exchange energy requires a difficult numerical integration. An alternate method is used to obtain the density matrix from an approximate partially collapsed Husimi matrix that gives the maximum entropy Husimi function as its diagonal. The results are exact for the harmonic oscillator ground state. Exchange energies calculated for H and the He isoelectronic series through C+4 show slight improvements over those calculated using a maximum entropy Wigner function.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390607
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  • 184
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    A density functional for the correlation energy, deduced in the framework of the correlation factor approach (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 23-32 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An approximate density functional is deduced from a wave function within the correlation factor method. The new functional does not include terms depending on the gradient of the density, but shows the simplicity of local density functionals without spin polarization. However, it includes correctly the inhomogeneity effects and, also, the nonlocal nature of an electronic system. The approach adopted here stresses the goodness of the expression taken by Colle and Salvetti for building a correlation factor and, at the same time, allows us to gain light on the nature of the deficiencies of those functionals obtained, up to now, from the perspective of the Hohenberg and Kohn theorem.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400105
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  • 185
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    SCF theory of molecular interactions (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 97-126 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Perturbation theory is used to analyze the interactions between two closed-shell systems in the SCF approximation. The effects of orbital overlap are included. The dominant terms through second order are identified, including electrostatic, penetration, polarization, charge transfer, and SCF dispersion effects. The basis set limit is studied so that basis set superposition contributions may be identified. Calculations are presented for He—He and Na+—H2O.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400110
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  • 186
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    Electronic Resource
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400201
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  • 187
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    The generalized Slater-Condon rules (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 201-210 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By relating the blocking structure of the relevant matrix of overlap-integrals to its cofactors, the Slater-Condon rules for the evaluation of an element of a matrix representation of an electronic Hamiltonian in a Slater determinant basis are generalized to the case where not all orbitals are orthogonal. This yields a set of 33 rules, which allows for an efficient implementation of the valence bond theory.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400204
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  • 188
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    Electronic Resource
    Quantum localization over a potential barrier (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 211-224 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ability of a harmonic barrier to support resonances is examined. Stabilization graphs calculated from box quantization have the features expected for resonances at an energy equal to the barrier maximum. The search for a wave packet of maximum lifetime leads also to this energy. These findings agree with the energies associated with the poles of the S matrix.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400205
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  • 189
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    Normal (decoupled) representation of electronegativity equalization equations in a molecule (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 265-285 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The decoupled (normal) representation of the electronegativity (chemical potential) equalization equations, in which the hardness tensor {ηij}={∂μi/∂Nj} becomes diagonal, is examined in the atoms-in-a-molecule (AIM) approximation; μi=∂E/∂Ni is the chemical potential of the i-th AIM, Ni is its electron population, and E is the system energy. All relevant chemical potential, hardness, softness, and Fukui function quantities corresponding to the normal electron redistribution channels, Qy, are discussed and expressed in terms of the canonical AIM parameters. The normal chemical potentials, μγ=∂E/∂Qγ, provide a natural classification of the normal modes into three groups: (a) acceptor normal modes (μa 〈 0, positive mode Fukui function, hardness, and softness), (b) donor normal modes (μd 〉 0, negative mode Fukui function, hardness, and softness), and (c) polarization normal modes (μp=0, zero mode Fukui function, hardness, and softness). The implications of the normal mode analysis for the theory of chemical reactivity are briefly summarized.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400208
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  • 190
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    Midgap levels of photoexcited conductive polymers. II. Detailed analysis of trans-polyacetylene (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 315-322 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have studied in more detail aspects of the soliton-antisoliton pair in a trans-polyacetylene chain based on our previous study of the midgap levels associated with the photogenerated oppositely charged soliton-antisoliton pair in conductive polymers employing the concept of the molecular orbital interaction (Part I of this study, this issue). The intersoliton distance has been estimated to be about 10 Å from the Pariser-Parr-Pople method. We have found that the energy gap between the midgap levels is estimated to be 0.45 eV, being significantly related to an additional photoinduced absorption.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400305
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  • 191
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    First-Order geometrical response equations for state-averaged multiconfigurational self-consistent field (SA-MCSCF) wave functions (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 361-378 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The first-order geometrical response equations for a state-averaged multiconfigurational self-consistent field (SA-MCSCF) calculation are derived. This derivation is carried through from first principles to final working equations suited for computer implementation. The final equations are expressed such that the energies and wave functions must be known only for the internal SA-MCSCF states. In the derivation, the special but important case where two or more internal states have equal weighting factors is treated in a manner fully consistent with all other cases. Except for introducing extra equations that are straightforward to solve, the case where two or more internal states have equal weighting factors introduces no new complications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400308
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  • 192
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    Ag vibrational levels of cyclobutadiene on a new potential energy surface (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 415-420 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: GVB/[5s3p1d/3s1p] energies were calculated for 31 geometries of cyclobutadiene in the D2h point group. These geometries differed in the values of the symmetrized internal coordinates for two CC stretching and one CCH bending modes. The data points were fitted to the expansions of in powers of . Variational calculations provided the following energies of the lowest Ag vibrational levels (with respect to the vibrational ground state): 4.4; 1161.2; 1162.3; 1304.0; 1322.8; 1920.3; and 1991.0 cm-1.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400313
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  • 193
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    Second-order perturbational treatment of normal coordinates in the string model for the hydration reaction of formaldehyde (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 435-456 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A perturbation theory for normal coordinates of nonadiabatic solvation is presented by means of the “string model” of chemical reactions. The dynamic normal coordinate is introduced for the perturbational treatment of the “intrinsic” normal coordinates that are orthogonal to the reaction path. The reaction is defined as the intrinsic reaction coordinate (IRC) that is treated as a string. The string is thrown in the external force field that acts as a nonadiabatic source of perturbation. As an application of the present treatment, the effect of a water molecule for hydration reaction of formaldehyde is calculated. A second-order perturbation effect for the enhancement of the reaction rate is found.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400402
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  • 194
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    Electronic Resource
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400501
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  • 195
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    Formulation of N- and v-representable density functional theory. IV. Non-Born-Oppenheimer approach (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 589-604 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Local-scaling transformations are employed in order to formulate a desity functional theory where both electrons and nuclei are treated quantum mechanically. Because of the properties of these transformations, the ensuing version of density functional theory is N- and v- representable. In particular, we study the effect of these transformations on both densities and generating wave functions, and as a result, a functional for the energy expressed in terms of the electronic and nuclear densities is constructed. Plausible physical approximations for simplifying this electronic-nuclear functional are considered, and upon variation of the fuctional with respect to the electronic and nuclear densities, a system of coupled Euler-Lagrange equations is obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400503
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  • 196
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    Pauling's criterion of bond strength and the relative bond lengths in molecule MLk (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 675-683 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper, the bond strengths, defined by Pauling, for a series of molecules in the type of MLk have been calculated by using the generalized method obtained from the maximum overlap method in a preceding paper and by using Pauling's pair-defect-sum approximation. A number of geometrical bonding situations are investigated. It is demonstrated why a previous study purporting to use of Pauling's criterion of bond strength to find that the axial bonds in trigonal bipyramidal ML5 are stronger than the equatorial bonds is incorrect. The results obtained from the two methods approach each other and are in good agreement with the experimental bond lengths, which show that Pauling's criterion is viable and that the pair-defect-sum approximation is indeed an excellent one that agrees with the maximum overlap method.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400509
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  • 197
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    Transforming Gaussians into Wannier functions using inversion of cyclic matrix (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 703-708 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: One-dimensional Gaussians are transformed into orthonormalized atomic orbitals (OAOS) using the inverse of the cyclic overlap matrix. During that process it was found that these OAOS are nothing but the Wannier functions and have properties similar to the Wannier functions obtained by Wannier himself from Gaussians using a different method. The present method gives rise to a better Wannier function with less distortion.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400512
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  • 198
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    Electronic Resource
    A graphical approach to configuration interaction studies in molecules using determinants of nonorthogonal orbitals (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 709-717 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A direct graphical approach is presented for the evaluation of matrix elements of a spin-free Hamiltonian between Slater determinants of nonorthogonal orbitals. The matrix element contributions are obtained by repeated use of N - 2 electron minors of the overlap matrix that are generated by independent looping of reduced N - 2 electron graphs for the α- and β-strings of the determinants. Because of the successive generation of the matrix contributions, the method is well suited for direct diagonalization schemes.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400513
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  • 199
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    Spin-orbit (core) and core potential integrals (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 773-780 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular integral formulas and corresponding computational algorithms are developed for the relativistic spin-orbit and core potential operators that are obtained from atomic relativistic calculations by means of the effective core potential procedure. Much use is made of earlier work on core potential integrals by McMurchie and Davidson. The resulting computer code has been made part of the ARGOS (Argonne, Ohio State) program from the C⋅OLUMBUS suite of programs, which computes the needed integrals over symmetry-adapted combinations of generally contacted Gaussian atomic orbitals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400606
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  • 200
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    Ab initio methods for large systemsProceedings from the Workshop on the Methodology of Evaluation of Integrals in LCAO Calculations at Argonne National Laboratories. (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 797-807 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Methods for calculations on extended systems are proposed, in which long-range Coulombic interactions are treated classically. The basic mode of description for the system is still in a quantum mechanical language, involving wave functions, Hamiltonians, etc. The electron density in a large molecular system is divided into suitable fragments, and the electrostatic potential generated by such a fragment at some distance away from it is then expressed by a generalized multipole expansion relative to a single point in space, conveniently taken as the center of charge distribution for that fragment. The computational effort required for evaluating the interactions involving those multipoles is modest and scales favorably (quadratically) with the size of the system. The remaining interactions, which need to be treated with conventional methods, i.e., with explicit one- and two-electron integrals, scale only linearly with size in extended systems. An important characteristic of the approach is that, while the approximations and shortcuts introduced have a clear physical origin, they can be justified on strict numerical grounds, such that calculated energies and other properties are identical to those obtained with conventional methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400609
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