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  • 1990-1994  (7,747)
  • 1980-1984  (5,936)
  • General Chemistry  (10,763)
  • Atomic, Molecular and Optical Physics  (2,918)
  • Nuclear reactions
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Material
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Year
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  • 101
    Electronic Resource
    Electronic Resource
    Electronic structure of paramagnetic clusters of transition metal ions.See [1] for Part 2. 3. Magnetic properties and scattered wave description of the electronic structure of the hexanuclear octahedral cluster [Fe6(μ3-S)8(PEt3)6] (BPh4)2 (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 903-918 
    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: Spin-polarized Xα-SW calculations of [Fe6(μ3-S)8(PH3)6]2+ as a model of the cluster [Fe6(μ3-S)8(PEt3)6] (BPh4)2 have been performed. The highest occupied energy levels are well separated from empty levels, and up to a maximum of eight electrons can be unpaired, giving a maximum spin state with S = 4. This electronic state is consistent with the magnetic data of [Fe6(μ3-S)8(PEt3)6](BPh 4)2, which have been interpreted using the Heisenberg-Dirac-Van Vleck exchange spin Hamiltonian. The S = 4 state arises from the magnetic coupling between five low-spin (Si = 1/2) and one intermediate-spin (S = 3/2) iron(III) center. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520416
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  • 102
    Electronic Resource
    Electronic Resource
    Geometrical and spectroscopical characterizations of some complex entities of aluminum(III) with fluoride ions by LDF-based calculations (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 927-934 
    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 structure of cryolite is investigated with a theoretical approach based on LDF calculations. In fact, experimental techniques for structural studies are difficult to perform in cryolite melts because of hard experimental conditions (high temperature, corrosiveness, etc.). Use of the DMol software allows us to determine the stabilities and the vibrational frequencies of AlF63-, AlF52-, and AlF4- isolated complexes. The results obtained compared with published experimental works confirm that AlF52- should be considered in the dissociation scheme of cryolite as previously evidenced by other authors. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520418
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  • 103
    Electronic Resource
    Electronic Resource
    Investigations of hydrogen-bonded systems: Local density approximation and gradient corrections (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 957-961 
    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 applicability of the local density approximation (LDA) and of corresponding gradient corrections (for the exchange and correlation energy) for the treatment of the hydrogen bond is investigated. As test systems, we consider the water dimer and the H2O…HX complexes (X = F, Cl, Br): Using an LCAO scheme, their equilibrium geometries and interaction energies are ćalculated and compared with experimental data and with other calculations. We obtain that the LDA gives the geometries in qualitative agreement with other data, whereas the energies are overestimated. The use of the gradient corrections (GC) according to Becke and Perdew leads to a significant improvement of the geometry, and especially of the interaction energies. The calculations indicate further that LDA + GC should also be able to describe weaker intermolecular interactions than the usual hydrogen bond. Finally, a short discussion of the charge distribution and the dipole moments of the H2O…HX complexes is performed. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520421
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  • 104
    Electronic Resource
    Electronic Resource
    A note on the number of spanning trees in buckminsterfullerene (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 525-528 
    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 “pedestrian” approach is used to enumerate the spanning trees in buckminsterfullerene. The approach is called “pedestrian” because calculations were carried out by hand and pocket calculator. The number of spanning trees obtained for buckminsterfullerene is 375,291,866,372,898,816,000, a number identical to the value reported by Brown et al. [J. Comput. Chem. 12, 1118 (1991)] who used a computationally more involved approach. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520846
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  • 105
    Electronic Resource
    Electronic Resource
    Theoretical study on the non-adiabatic photodissociation process of argon cluster ions Ar7+ (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 529-539 
    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 photodissociation process of argon cluster ion is studied by using the molecular dynamics method with non-adiabatic transitions. The potential energy surfaces and the electronic states are calculated with the diatomics-in-molecules (DIM) hamiltonian. The initial configurations are sampled from the classical trajectory paths on the potential energy surface of the electronic ground state. The non-adiabatic process is treated with the scheme proposed by J. C. Tully [J. Chem. Phys. 93, 1061 (1990)] with a slight modification. The method is applied to the photodissociation process of Ar7+. The calculated kinetic energy distribution and angular distribution of the photofragment are in good agreement with the ex-perimental results, but the branching ratio between Ar+ and Ar2+ fragment ions is not. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520847
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  • 106
    Electronic Resource
    Electronic Resource
    SC-MEH-MO calculations on lanthanide systems. I. Sm(Cp*)2, bis(pentamethyl-cyclopentaldienyl)Sm(II) (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 565-569 
    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: SC-MEH-MO calculations with electron repulsion correlation and configuration interaction included, have been carried out on Sm(Cp*)2 in both its linear and bent geometrical forms. Except for relatively small factors, there are virtually no major differences in the electronic structures of the two comfomers. In both cases, the bonding is found is to be very clost to being nearly totally ionic. An estimation of the ionic bond energy is made and discussed. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520850
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  • 107
    Electronic Resource
    Electronic Resource
    Structural and electronic studies of Ga3As3, Ga4As3, and Ga3As4 (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 571-577 
    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 self-consistent-field calculations are performed on Ga3As3, Ga3As4, and Ga4As3 clusters. Geometries, electron affinities, ionization potentials, and bondings are analyzed for these clusters. Geometry optimizations using analytic energy gradients followed by single point MP2 calculations are performed to decide for the equilibrium structure. The alternation pattern observed for the ionization potential and electron affinity are verified for these clusters after correlation energy is included. Our results are compared with previous theoretical and experimental calculations. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520851
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  • 108
    Electronic Resource
    Electronic Resource
    Relativistic density-functional studies of naked and ligated gold clusters (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 595-610 
    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: Electronic structure investigations on a broad range of gold compounds, including naked and ligated gold clusters, are reviewed. The calculations have been carried out with a recently introduced relativistic variant of the linear combination of Gaussian-type orbitals density-functional (LCGTO-DF) method which affords all-electron investigations for very large systems. The accuracy of the method will be evaluated for the gold dimer. Then the electronic structure of the naked cluster Au55 is studied, both in Ih and Oh symmetry. Nonrelativistic and relativistic results obtained by the present method are compared to those of the much simpler jellium model. Since triphenylphosphine is among the most common ligands in gold chemistry a series of mononuclear gold phosphine compounds MeAuPR3 with increasingly complex ligands PR3 (R = H, CH3, C5H6) is discussed. The calculations reveal the success and the limitations of simpler phosphines often employed as model ligands in theoretical studies. Some aspects of the phosphine gold interaction in these simpler compounds carry over to the main group element centered gold clusters. Thereby one arrives at a rationalization of the particularly high stability of the carbon-centered octahedral cluster cation [(R3PAu)6C]2+ as compared to the neighboring isoelectronic boron and nitrogen-centered clusters. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520853
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  • 109
    Electronic Resource
    Electronic Resource
    On the role of doping in high-Tc superconductorsThis work was partly supported by the US Office of Naval Research, and partly by the Natural Science and Engineering Research Council of Canada. (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 687-693 
    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: High-Tc superconductors (HTSCS) are usually obtained by doping electron donors or acceptors into parent materials. The actual role played by doping is still uncertain with various interpretations. The present electronic structure study provides some hints which may help to solve the mystery. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520861
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  • 110
    Electronic Resource
    Electronic Resource
    A quantum monte carlo simulation of the two-dimensional H2 molecule (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 50 (1994), S. 401-410 
    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 problems connected with the simulation by the diffusion quantum Monte Carlo method of atomic and molecular systems in the two-dimensional (2D) space have been investigated on the 1 2S and 2 2S states of the hydrogen atom and on the 1 1S and 1 3S states of the helium atom, assuming r-1 Coulomb interactions between the particles. The potential surface of the 1Σg+ state of the 2D hydrogen molecule has been calculated in the range 0.1-1.5 bohr: A dissociation energy of 1.2703 Hartrees is found at the equilibrium distance of 0.3639 bohr. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560500604
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  • 111
    Electronic Resource
    Electronic Resource
    Relativistic quantum defect calculations on the copper isoelectronic sequence (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 50 (1994), S. 411-428 
    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 quantum defect orbital (QDO) method and its relativistic (RQDO) counterpart have been employed in this work to compute oscillator strengths for several fine-structure transitions in members of the copper isoelectronic sequence up to Z = 92. The RQDO results are found to be in quite good agreement with the best estimates derived from other sources, whenever the comparison is possible. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560500605
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  • 112
    Electronic Resource
    Electronic Resource
    Masthead (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994) 
    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.560510101
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  • 113
    Electronic Resource
    Electronic Resource
    International journal of quantum chemistry - A journal devoted to quantum theory and computations in chemistry, condensed matter physics, and biology. Editorial - program and policies (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 1-2 
    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.560510102
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  • 114
    Electronic Resource
    Electronic Resource
    Spatially confined simple quantum mechanical systems (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 50 (1994), S. 429-444 
    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 two simple quantum mechanical system, i.e., harmonic oscillator (HO) and hydrogen atom (H) trapped inside the wells is performed. The influence of the spatial confinement on the energy spectra of both systems is investigated. An analytically solvable model of the well potential is presented in the case of the HO. A central and noncentral localization of HO in the well is discussed. The results are used to explain some reported anomalous experimental data on the porphine IR spectrum. The case of hydrogen atom is studied by solving the problem of the electron in the potential V = Z/R cot r/R. An exact formula for the energy is derived for s states. For others, analytically nonsolvable symmetries, a formula with correct asymptotic behavior is proposed. The results are compared with some numerical calculations for spherical rectangular well and an extension to many-electron atoms is also presented. The effect of breaking degeneracy and of ordering energies of H in a different way than in the case of many-electron systems is broadly discussed. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560500606
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  • 115
    Electronic Resource
    Electronic Resource
    Nonadiabatic NO expansions for the ground state wave function of H2+ (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 3-11 
    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 article, direct calculations of nonadiabatic NO expansions for the ground-state wave function of H2+ are given, as predicted by Bishop and Cheung. Two methods are presented, i.e., an analogon to the Ahlrichs/Driessler procedure and a gradient method, both originally developed to calculate natural orbitals for two-electron systems. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560510103
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  • 116
    Electronic Resource
    Electronic Resource
    Full configuration interaction study of the ground state of closed-shell cyclic PPP polyenes (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 13-25 
    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: Full configuration interaction (FCI) calculations are reported for the closed-shell cyclic polyenes CNHN (N = 6, 10, 14, 18) in the Pariser-Parr-Pople (PPP) approximation, as a function of the hopping parameter β. A wide range of values of β is considered, from a highly correlated situation, β = 0, to a very weakly correlated limit, β = -10 eV. An estimate of the role of higher than two-body connected cluster components was done, through a partial (i.e., limited to two-body terms in the exponent) cluster analysis performed on the FCI wave function. The comparison with the approximate coupled pair theory that accounts for quadruply excited clusters [see P. Piecuch and J. Paldus, Theor. Chim. Acta 78, 65 (1990)] shows a good agreement in the whole range of the hopping parameter, particularly when the contribution of connected triples excitations is also taken into account. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560510104
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  • 117
    Electronic Resource
    Electronic Resource
    Masthead (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994) 
    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.560510401
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  • 118
    Electronic Resource
    Electronic Resource
    A density-functional method for calculating atomic polarizabilities: Application to negative ionsThis article was originally submitted for inclusion in the issues dedicated to Dr. Robert G. Parr. (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 201-209 
    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 recently proposed a variational method for determining static polarizabilities that uses the ground-state density, rather than the orbitals, of the system for calculations. Thus, the method is different from, and numerically easier than, the perturbation theory approach in which changes in each of the single-particle orbitals have to be obtained self-consistently. For neutral atoms and cations, it leads to results that are comparable to the results obtained by the perturbation theory. In this article, we apply this method, employing Hartree-Fock densities, to obtain polarizabilities for negative ions and show that for negative ions also the results are quite accurate. Thus, the method may prove useful in making quick and accurate estimates of the polarizabilities of more complex systems where orbital based self-consistent calculations become quite complicated. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560510404
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  • 119
    Electronic Resource
    Electronic Resource
    Modified valence indices from the two-particle density matrix (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 187-200 
    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 modified ionic and covalent valence indices are introduced, defined in the framework of the two-particle density matrix, with respect to the reference state of separated atoms or ions (SAL). They include only quadratic contributions in changes of the molecular charge-and-bond order matrix elements, relative to the SAL. General properties of the modified valence indices are examined and illustrative qualitative results for model systems are presented. Numerical UHF SCF MO valence data for selected diatomic and triatomic molecules are reported and interpreted in terms of the valence saturation effect and the ionic vs. covalent valence competition. A three-orbital valence model of a symmetric transition state of the bond-forming-bond-breaking reaction supports the BEBO model postulate of preservation of the total “bond order.” The model predictions are compared with the UHF numerical values. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560510403
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  • 120
    Electronic Resource
    Electronic Resource
    Masthead (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994) 
    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.560510501
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  • 121
    Electronic Resource
    Electronic Resource
    Self-consistent second-order screening in many-body theory (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 389-396 
    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: Self-consistent screening arises in all many-body problems where one-particle equations containing functionals of the solutions are considered. In the theory of simple metals, e.g., these one-particle equations are usually solved to second-order perturbation in the crystal pseudopotential and to first order in the screening. However, higher-order screening terms have a sizable effect on the form factors, the electron charge density, and the screened pseudopotential. The effects of second order are presented for the bcc simple metals Na and Ba. A nonlocal exchange-correlation potential has been used since local density approximations such as ρ1/3 cause difficulties in the electron-electron dielectric function. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560510606
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  • 122
    Electronic Resource
    Electronic Resource
    Developments in multicenter molecular integrals over STOs using expansions in spherical harmonics (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 417-423 
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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 strategy of using expansions in spherical harmonics of displaced Slater-type orbitals for the evaluation of multicenter molecular integrals is reviewed and projected. Our Löwdin α-function method is augmented by computer algebra and C, E, and F matrices with rational elements. This permits exact evaluations of each term in an infinite sum using a commercial computer algebra program to investigate the three-center nuclear attraction integral. Each term (harmonic potential) is important for proposed use in numerical evaluations of multicenter integrals. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560510609
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  • 123
    Electronic Resource
    Electronic Resource
    A new model of a molecule based on the soft body (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 439-445 
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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 basic idea of the deformable or soft-body model of a molecule, which starts from a new definition of the reference configuration, is presented. It is shown that this model introduces into the Hamiltonian a new part that describes deformation energy of a molecule brought about by its rotation. This part leads to nonlinear terms, whose numerical values were compared with the semiempirical approach. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560510611
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  • 124
    Electronic Resource
    Electronic Resource
    Thermal reaction rates with a two-point flux-flux correlation function (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 465-472 
    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 thermal rate constant of a bimolecular reaction is shown to be expressible as the time limit of the time integral of a correlation function involving the reactive flux at two different points along the path leading from reactants to products. This extension provides some additional flexibility in the finite basis-set representation of the rate given by Miller-Schwartz-Tromp [J. Chem. Phys. 79, 4889 (1983)]. Some of the features of this expression are examined in the case of one-dimensional Eckart barrier. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560510613
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  • 125
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    Electronic Resource
    Application of many-body perturbation theory in the localized representation for the all-trans conjugated polyenes (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 127-133 
    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 self-consistent field (SCF) calculations are performed with the standard 6-31G* basis set for all-trans conjugated oligomers C2n+2H2n+4. The canonical occupied and virtual molecular orbitals (MOs) are separately localized by unitary transformations. Due to the localization, the perturbation operator is partitioned into two-particle and into single-particle terms; the MBPT is, therefore, a double-perturbation expansion in this case. By using the localized representation of the MBPT, the correlation energy contributions can be partitioned into local and nonlocal effects. It can be shown that the local effects are very important and well transferable, which makes possible the calculation of the correlation energy of larger molecules if the localized molecular orbitals (occupied and virtual) of smaller related molecules are known. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520113
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    Masthead (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994) 
    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.560490101
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    The onset of classical chaos in atom-surface scattering (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 515-525 
    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 relationship between surface rainbows and the onset of classical chaos in atom-surface scattering is discussed. The principal focus is the onset of chaos as a function of experimentally controllable parameters. The correspondence between the classical trapping and quantum mechanical selective adsorption resonances is briefly discussed. The connection with the more mathematical work of Grebogi and co-workers is also considered. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520222
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    Theoretical study of many-body effects in the photoelectron spectra of unsaturated hydrocarbons (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 527-548 
    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 theoretical investigation on the core and valence photoelectron spectra of unsaturated hydrocarbons of increasing complexity, ethylene, trans-butadiene, and trans-hexatriene, has been performed in order to analyze the role of the most important many-body effects on the spectral features and the evolution of these effects along the series. The capability of various configuration interaction (CI) schemes to interpret both the core and the valence ionization satellite structures has been pointed out. The 3h-2v(π)-1p and 2h-1p CI schemes employed, together with an accurate choice of the basis set and the explicit inclusion of the relaxation, has proven to be very useful tools for this kind of study, being sufficiently accurate to explain the most important correlation features and extendible, at the same time, to longer chain systems. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520223
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    The interaction of chemical bonds. III. Perturbed strictly localized geminals in LMO basis (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 563-574 
    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 formalism of strictly localized geminals (SLGs) is summarized. It is shown that the SLG wave function serves as an appropriate multiconfigurational reference state that can easily be improved by perturbational, CI- or coupled cluster-type procedures. The possibility of expanding the geminals in the basis set of localized Hartree-Fock molecular orbitals (LMOs) is discussed. Sample calculations on H4, CH4, H2O, and He…He systems are reported. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520225
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    Computation of algebraic formulas for wigner 3-j, 6-j, and 9-j symbols by maple (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 593-607 
    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: Three programs capable of computing algebraic formulas for Wigner 3-j, 6-j, and 9-j symbols have been written in the Maple* program language. These programs can also compute numerically exact values of 3-j, 6-j, and 9-j symbols. © 1994 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520303
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  • 131
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    Path integral's semiclassical quantification (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 609-616 
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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 discuss here a new formal way to evaluate the electronic correlation energy of a molecular system. We use the path integral formalism in the regime of the molecular orbitals. The semiclassical approximation in this procedure is an expansion of the effective action Seff around the classical closed orbits into generalized phase space keeping only the quadratic fluctuation. Thus, after some transformations, we apply to the final expression analogous conditions to the Bohr-Sommerfeld quantification rules. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520304
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    Announcement (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994), S. 59-61 
    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.560490108
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  • 133
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    Three stages of optimization and simple correlated wave functions (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994), S. 45-57 
    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 advocated to carry out an optimization procedure, which is based upon the variational method, in such a way that the optimum values of the variational parameters are expressed as functions of physical constants, such as the atomic number, Z. The three stages involved in this treatment are illustrated by the optimization of nine correlated wave functions, which describe the ground states of atomic two-electron systems. An analysis of the Z-expansions of the total energies associated with these functions leads to the concept of a class of variational functions. The performances of functions belonging to the same class differ only marginally, especially at larger values of Z. Consequently, the concept of class may be used to bring some order in the plethora of variational functions. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560490107
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    Masthead (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994) 
    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.560490301
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  • 135
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    Reaction path as a gradient line on a potential energy surface (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994), S. 105-127 
    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 reaction path is shown to be always a gradient line on a potential energy surface (PES) of a molecule. The properties of gradient lines on the PES are elucidated. Correct symmetry conservation rules along the gradient line are derived. The behavior of the gradient line on a PES with different topologies are considered. © 1994 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560490206
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    Robert G. Parr (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994), S. 131-131 
    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.560490303
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  • 137
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    Introduction to a paper symposium on “the role of Quantum Chemistry as a foundation for the principles of chemistry” (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994), S. 129-130 
    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.560490302
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  • 138
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    The effects of nonlocal gradient corrections in density functional calculations of hydrocarbon radical hyperfine structures (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 879-901 
    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: Ground-state equilibrium geometries and hyperfine structures of a number of organic neutral and charged radical compounds are computed using the linear combination of Gaussian-type orbitals-density functional theory method. In addition to the local spin-density approximation, we also use two different nonlocal (gradient corrected) schemes for the calculations of the exchange and correlation potentials. The different functional forms are found to generate slightly different total and unpaired spin-density distributions in the molecules, and as a result, the computed isotropic hyperfine coupling constants vary markedly. The smallest variations are found for the hydrogens, where the results are generally in satisfactory agreement with experiment. For the carbon atoms, however, large differences in isotropic coupling constants are observed. The anisotropic hyperfine structures are generally very well described at all levels of theory. © John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520415
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  • 139
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    Ground-state properties of CdxSn1-xTe: The role of d-electrons (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 919-926 
    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: Within the framework of density functional theory (DFT), we calculate the ground-state electronic properties of CdxSn1-x Te using norm-conserving pseudopotentials in connection with the local density (LDA) and virtual crystal approximation (VCA). Our particular interest is in the influence of the Cd-4d and the Sn-4d electrons by comparing results obtained with pseudopotentials, which either consider the d-electrons explicitly or in the frozen core. In the mixed crystal system CdxSn1-x Te, the transition from a ten- (x = 0) to an eight-electron (x = 1) system is realized, which is accompanied by a change of the crystal structure from rock salt (SnTe) to zinc blende (CdTe). By calculating the ground-state energies, we find the equilibrium lattice constant as the function of x and the bulk modulus, as well as the crossover value of x for the transition from rock-salt to zinc blende. The calculated lattice constants and bulk moduli are in much closer agreement with experimental data if the d-electrons are taken into account explicitly, whereas the crossover is rather insensitive with respect to the d-electrons. In view of the electronic charge density, we demonstrate the decrease of ionicity for increasing x. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520417
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  • 140
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    Symmetry breaking and its influence on the correlation energy for CF4+ and CF32+ ions (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 947-956 
    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 symmetry breaking in three open-shell systems: CF4+ (D2d and C2v) and CF32+ (D3h) molecular ions. These different Hartree-Fock solutions are employed as starting points to calculate the correlation energy of these ions with perturbative, configuration interaction, and density functional methods. When symmetry-broken or symmetry-adapted wave functions are used, the correlation energy obtained with each method changes the order of stability of CF4+ for a determined symmetry. Density functional methods produce higher correlation energies although they do not alter the order of stability of Hartree-Fock calculations. The behavior of correlation energy with different methods and the characteristics of the symmetry of wave functions are compared. A study of appearance energies for three different channels of the decomposition reaction of ionized carbon tetrafluoride are considered by using different methods with symmetry-broken or symmetry-adapted wave functions to calculate correlation energies. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520420
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  • 141
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    Application of second-order density functional methods to the calculation of the LiFH potential energy surface (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 935-945 
    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: Second-order density functional methods are used to introduce the electron correlation in Hartree-Fock (HF) ab initio electronic energy calculations of three-dimensional potential energy surfaces (PES). We analyze the behavior of these methods in PES calculations by applying them to the Li + FH reaction, which has been considered a prototype of the elementary atom-diatom reactions. This system has been studied also by the usual techniques, allowing a point-by-point (for a total of 317 grid points) comparison for the lowest 2A' adiabatic state. In particular, we compare the results obtained using the HF, Møller-Plesset (MP3 level), and configuration interaction (CISD and MRDCI levels) methods with the corresponding results obtained using the Colle-Salvetti (CS) and Moscardó-San Fabián (MSF) procedures using the HF results as the starting point. We found that the CS and MSF procedures support the prediction of a shallow well in the entrance channel that deepens slightly away from collinearity and disappears for a bond angle Θ 〈 74°. We also found that the constrained saddle-point positions remain essentially constant from Θ = 180°-90° and are clearly in the exit channel as for the MRDCI approach (corresponding to the best results). In conclusion, there is a good overall agreement, but there is a question in which this agreement is less pronounced: the heights of the saddle points including the transition state. In particular, the transition-state height is about 3 kcal/mol higher than the more accurate value obtained with the MRDCI approach. However, the second-order density functional methods have been capable of reducing the HF barrier from 18 to 9 kcal/mol (all of these values obtained by spline interpolation), the latter value being very similar to the CISD result. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520419
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    Density functional theory: An effective theoretical tool for the study of σ radicals (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 963-971 
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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 structures, harmonic force fields, and hyperfine coupling constants of a number of representative σ radicals have been investigated by the density functional approach including nonlocal corrections. Scaling of CH bond lengths and stretching constants leads to accurate structures and force fields. Hyperfine coupling constants reach, at least, the level of the most sophisticated conventional post-Hartree-Fock models. This suggests that the density functional approach is a promising theoretical tool for the study of relationships between structure and spectroscopic properties of large free radicals. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520422
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  • 143
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    Bonding of acetylene to copper atom, dimer, and trimer (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 973-985 
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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 bonding of acetylene to copper atom, dimer, and trimer was investigated with a Kohn-Sham density functional approach. Full geometry optimization yielded the equilibrium structures of various CunC2H2 species. Gradient corrections were included in the calculation of binding energies (BE). The Cu - C2H2 complex was found to have a Cs structure and a BE of 10 kcal/mol. Three isomers of Cu2C2H2 have similar total energies: a C2v end-bonded structure with a BE of 18 kcal/mol, and two 1,2-dicupro ethylene isomers - a cis form with a BE of 12 kcal/mol and a trans form with a BE of 15 kcal/mol. Two stable C2v isomers of Cu3C2H2 were found. In both isomers, the Cu3 ring relaxes from its isosceles structure, with two short bonds (2.247 Å) and one long bond (2.478 Å), and adopts a nearly equilateral geometry. In one isomer of Cu3C2H2, the acetylene is bonded to one apex of the Cu3 ring with a BE of 29 kcal/mol. In the other, it is bonded to two copper atoms of one side of the Cu3 ring with a BE of 33 kcal/mol. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520423
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    Self-consistent calculations of total energies and charge densities of solids without solving the band-structure problem (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 987-992 
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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 have used a recently proposed method allowing a direct calculation of the total energy and of the charge density of a crystal to determine the equilibrium lattice parameter, the cohesive energy, and the bulk modulus of MgO and CaO. The results that we have obtained are compared with those of a variety of band-structure calculations as well as with the experimental data. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560520424
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    Theory of relaxed density matrices: Application to second-order response properties (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994), S. 371-381 
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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 evaluation of second derivatives of the electronic energy for nonvariational wave functions using an energy functional is discussed. It is shown that, in certain cases, the formation of the first-order relaxed density matrix leads to an efficient algorithm for the calculation of second-order response properties. Detailed formulas are given for second-order Møller-Plesset perturbation theory. © 1994 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560490405
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    Potential energy surfaces of carbon dioxide (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994), S. 409-427 
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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: Several bent valence states of CO2 are characterized by means of full-valence-space MCSCF calculations. The ground state potential energy surface exhibits a double well corresponding to a ring minimum, with C2vsymmetry (1A1) and a 73.1° OCO angle, in addition to the linear (1σg+) global minimum. The transition state for the ring opening process, which has a barrier of 12.1 kcal/mole with respect to the ring minimum, is however found to have Cs symmetry. Double minima are also shown to exist for the 1A2, 1B1 and 1B2 excited states. However, in these cases all minima are bent. Cross sections through the ground state potential energy surface corresponding to the two collinear exchange reactions O(1D) + CO(1σ+) → OC(1σ+) + O(1D) C(3P) + O2(3σg-) → CO(1σ+) + O(1D) are also calculated and their energy contour maps are reported. The latter reveals the existence of a stable linear intermediate with the structure COO. © 1994 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560490408
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    Protonation of fused aromatic systems: Ab initio study of some model Wheland intermediates (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994), S. 383-396 
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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: Structure and properties of Wheland's intermediates are studied in some model systems. The effect of the annelated small ring is simulated by bending two vicinal CH bonds in benzene toward each other. The extent of bending describes the ring-size effect of a small fused fragment molecule. The electrophilic substituent is represented by a proton. Calculations at the HF/6-31G* and MP2/HF/6-31G* levels of sophistication confirm the Mills-Nixon (MN) hypothesis. It is conclusively shown that ß-complexes are more stable than are α-protonated species. The results are interpreted in terms of the ground-state density distribution dictated by rehybridization and of the transition structure π-electron redistribution triggered by protonation. Their effects are additive to a large extent as far as CC bond distances are concerned. Energetic properties are determined by the interplay of two characteristic π-electron localization patterns, one caused by the initial angular strain and the accompanying rehybridization related to the ground state and the other one occurring during formation of the proton σ-complex. This interplay destabilizes α-intermediates relative to ß-intermediates. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560490406
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    Orbitals expanded in slater functions with single-exponent by shell and by subshell (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 397-405 
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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: Slater-type orbitals (STOs) with a single-exponent by shell or by subshell have been constructed to reduce the number of integrals evaluated in the electronic calculations. The expansion of orbitals in these new basis sets has been carried out in detail for the ground state of the Ne atom. We have carried out a study of STO basis sets with a different size for this atom that could help to propose empirical rules for the selection of these basis sets for other atoms. The usefulness of STOs with single-exponent by shell and subshell and the splitting of s and p functions are discussed. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560510607
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    Improvement of methods for molecular dynamics integration (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 407-415 
    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 application of symplectic implicit Runge-Kutta (RK) integration schemes, the s-stage Gauss-Legendre Runge-Kutta (GLRK) methods of order 2s, for the numerical solution of molecular dynamics (MD) equation is described. The two-stage fourth-order GLRK method, the implicit midpoint rule, and the three-stage diagonally implicit RK method of order four are studied. The fixed-point iteraction was used for solving the resulting nonlinear system of equations. The algorithms were applied to a complex system of N particles interacting through a Lennard-Jones potential. The proposed symplectic methods for MD integration permit a wide range of time steps, are highly accurate and stable, and are thus suitable for the MD integration. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560510608
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  • 150
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    Quadrupole and octupole Cauchy moments of the atoms through argon (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994), S. 449-461 
    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: Quadrupole and octupole Cauchy moments of the atoms through argon are calculated using the hydrodynamic formulation of time-dependent Kohn-Sham theory. The exchange-correlation energy density functional is approximated by a gradient expansion for atoms that has an explicit dependence upon the number of electrons. The first-order corrections to the Kohn-Sham amplitudes and phases are found by seeking variational solutions of the derived sequential set of functionals. The trial functions employed contain both linear and nonlinear variational parameters and are thus flexible enough to provide rapid convergence to the multipole polarizabilities. The resulting Cauchy moments provide information that allows the calculation of various properties that result from the linear interaction of atoms with a time-varying electric field. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560490410
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  • 151
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    Natural polyelectron population analysis (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 1127-1144 
    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 method to perform a polyelectron population analysis of correlated molecular orbital wave functions on the basis of natural atomic orbitals (NAOs), as given by Weinhold, is presented. The method allows calculations of the probabilities of finding various types of electronic events occuring in some target AO positions, including the contributions of ionic and covalent resonance structures. This method is general and neither the theory nor the developed algorithm limit the number of electrons and holes that can be considered. Thus, the analyzed MO wave function can be a usual CI or a MCSCF one, and apart from Weinhold's NAOs. any other type of orthogonal AOs can be used as analyzers, provided that these AOs are linear combinations of the SCF-AOs. Numerical applications are given for ethylene, formaldehyde, butadiene, and acroleine, by adopting various AO basis-set levels (STO-4G, 4-31G, and 6-31G) and by analyzing correlated wave functions (CISD). Improvements in the polyelectron populations when increasing the quality of AO basis sets and the corresponding valence NAOs are revealed by several examples. Furthermore, it is shown that the electroegativity of oxygen in acroleine only has an effect on contributions of ionic and covalent resonance structures, but not on delocalization of the double bonds. 1993 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520502
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  • 152
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    Improved tight-binding method (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 1199-1218 
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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 improved tight-binding method, taking into exact account the kinetic energy oerator, is proposed. The potential part of the Hamiltonian is represented by its matrix elements on some set of localized functions (like the LCAO method). The spectrum and the density matrix are determined by means of solving the nonlinear eigenvalue problem. © 1994 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520506
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  • 153
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    Two types of Kramers rate equations for reactions in condensed media (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 1219-1228 
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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: Two cases of bilinear coupling of a particle to a medium are compared. They differ in that one of the mediums does not modify the particle potential, whereas the other does. Two corresponding kramers-type rate equations for adiabatic reactions are derived directly from a dynamic rate theory and interpreted from the view of the stochastic theory. Both equations become identical in the weak coupling limit. Their relations to transition-state theory are also discussed. Corresponding results for nonadiabatic reactions are considered. © 1994 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520507
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  • 154
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    Functional derivative δE/δρ in calculation of chemical potential for the Kohn-Sham electronic system (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 569-575 
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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: A method for finding the chemical potential for an electronic system with density ρ = Σρi represented within the Kohn-Sham approximation is proposed. To find the chemical potential of the system under consideration, we propose to refer to the definition μ = δE/δρ and to apply the mathematical properties of functional derivatives. Particularly, in the case examined, the result μ = μ(r) ≠ const has been obtained, which may be explained in the framework of the calculus of variation. Taking the limit limr→∞ μ(r) as the best approximation to the proper equilibrium chemical potential of a free atom, one obtains μ = -I, where I denotes first ionization energy. A possibility of further applications of the proposed method in relation to crystalline systems is also discussed. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560510621
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  • 155
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    A comprehensive approach to molecular charge density models: From distributed multipoles to fitted atomic charges (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 17-37 
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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: Some alternative methodologies for the construction of reliable charge density models, involving distributed multipole schemes, potential fitted atomic charges, and a recent approach proposed by Ferenczy, are compared and analyzed critically. Ferenczy's method, which combines the distributed multipole description and the classical least-squares fit, allows one to get an insight into the well-known shortcomings of standard potential- or field-derived atomic charge models. It is now demonstrated that the conformational dependence of fitted point charges is not exclusively due to through-space inductive effects, but that it can be partly rationalized by the reorientation of the atomic multipoles. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520104
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  • 156
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    Theoretical evolution of the third-order molecular polarizabilities as a function of chain length in thiophene and pyrrole oligomers (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 39-48 
    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: On the basis of INDO (intermediate neglect of differential overlap)/MRD-CI (multireference determinant-configuration interaction) calculations, the SOS (sum-over-states) formalism is applied to calculate the third-order polarizabilities, γ, in thiophene and pyrrole oligomers. For both types of oligomers, the chain-length dependence of γ can be divided into three regimes: Describing γ as a power law of the number of rings (N), we observe that the power value first strongly increases with N, than reaches a nearly constant value (power regime), and, finally, decreases toward one, indicating the appearance of a saturation regime. Very good agreement with the experimental evolution has been found in the case of the oligothiophenes. The comparison of the results obtained for the two types of oligomers indicates a lower polarizability in the oligopyrroles. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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  • 157
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    On the determination of effective one-electron Hamiltonians to be used for studying large molecules (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 59-70 
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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 possibility of defining a one-electron effective Hamiltonian in the form of a Hückel-type matrix, taking into account the effect of the environment of the atoms in different molecules (the E2HT). It is found that the appropriate basis set in which this Hamiltonian is defined can be determined by using diatomic fragments. Concerning the matrix elements themselves, the appropriate information can be taken in fragments with a size similar to that of ethane. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520107
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  • 158
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    Theoretical study of the conjugation length effect on the electronic and second-order nonlinear optical properties of amino-nitro diphenylacetylenes (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 89-96 
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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 presnet a theoretical study of the effect of the conjugation length on the electronic properties and second-order molecular polarizabilities β in p-amino-p′-nitrodiphenylacetylene molecules where the number of triple bonds in the conjugated segment varies from 1 to 4. The β values are calculated via an intermediate neglect of differential overlap/single configuration interaction (INDO/SCI) sum-over-states (SOS) approach. We test the convergence of the SOS method and the validity of the two-state model to describe the β response. The results indicate that increasing the conjugation length results in a decrease of the charge transfer within the molecule. The two-state model is shown to break down as the conjugated segment extends to four triple bonds; this is due to the appearance of several low-lying nearly isoenergetic excited states that significantly contribute to the β response. The theoretical results are in excellent agreement with recent experimental data. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520109
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  • 159
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    MBOHO calculations of C—H stretching frequencies in hydrocarbons and heterosubstituted hydrocarbonsThe project was supported by the National Natural Science Foundation of China and the Excellent University Teacher's Foundation of the State Education Commission. (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 109-116 
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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: Based on the generalized relationship for calculating the nuclear spin-spin coupling constants and the correlation of the bond stretching frequencies with the coupling constants, a novel generalized reationship, which includes the contributions of not only the hybrid orbitals, but also the net atomic charges, is introduced for calculation of the bond stretching frequencies and employed to elucidate the C—H stretching frequencies in hydrocarbons and heterosubstituted hydrocarbons on the basis of the MBOHO calculation employing the CNDO/2 approximation. By use of the obtained concrete realtionships, one can get different νCH value for the C—H bonds existing in different chemical environments, which is coincident with chemical intuition. The calculated numerical results show that for hydrocarbons the contribution of the net atomic charges can be neglected, but it is necessary for heterosubstituted hydrocarbons to include the contribution of the net atomic charges to the C—H stretching frequencies. The calculated C—H stretching frequencies are in good ageement with the experimental data, which shows its reasonableness. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560520111
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    Core photoionization satellites in fullerence and related model systems (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 135-146 
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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 so-called shake-up satellites accompanying C1s photoionization in C60 have been studied theoretically by means of INDO/CI. It is found that the lowest shake-up satellites in C60 correspond to global charge-transfer excitions that move charge from the opposite side of the fullerence cage to the core-hole region, whereas higher-energy satellites tend to move charge from regions nearer to the core hole. Analogies are drawn, with, on the one hand, smaller model molecules such as napthalene and acenaphtylene and, on the other hand, infinite systems such as graphite. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520114
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  • 161
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    Construction of linearly independent relativistic symmetry orbitals for finite double-point groups including time reversal symmetry (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 1369-1372 
    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.560520611
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  • 162
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    X-ray scattering by water molecules studied by using synchrotron radiation (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 1339-1348 
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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 energy spectra of free water molecules were measured at scattering angles 2θ ranging from 10.5° to 75.7°, using an angle-dispersive-type diffractometer and synchrotron radiation as an X-ray source. A silicon (111) monochrometer was used to obtain incident X-rays with the wavelengths of (1.543/n) Å (n = 1,3,4,5). Observed inelastic scattering peaks are clearly separated from eleastic ones at s values [s = (4π/λ) sin Å] larger than 8 Å-1. The increase of the separation with an increasing s value was consistent with the classical theory of the Compton shift. The total (elastic plus inelastic) intensities were obtained over a range of s = 0.74-5.0 Å-1. Experimental difference intensities Δσee and Δσne were obtained separately by combining the X-ray and high-energy electron scattering data. The experimental results are in reasonable agreement with the theoretical intensities calculated from SCF and CI molecular wave functions with a basis set of double-zeta plus polarization functions. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520609
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  • 163
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    Spectroscopic properties and potential energy curves of some low-lying electronic states of AlO, AlO+, LaO, and LaO+: An ab initio CASSCF studyThis article was originally submitted for inclusion in the issues containing the Proceedings of the First Congress on Theoretical Chemical Physics. (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 1329-1338 
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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: Results of CASSCF state-averaged calculations on the lowest electronic states of LaO and LaO+ are reported in this work. For comparison, some low-lying electronic states of AlO and AlO+ are also reported. The ground state of LaO was found to be the X2Σ+ (Re = 1.987 Å, ωe = 794 cm-1) with a low-lying A2Δ excited state. Five more excited states below 26000 cm-1 were found. The first ionization potential (IP) is found at 5.16 eV, resulting in an X1Σ+ ground state for the LaO+ diatom, in opposition to AlO+ for which an X3 Π ground state has been found. Analysis of the wave functions, dipole moments, and Mulliken populations reveal that the bonding is quite ionic in both systems. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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  • 164
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    On the accuracy of molecular properties by coupled-cluster methods for some difficult examples: Oxygen atom, iron atom, and cyano radical (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 211-225 
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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: Coupled-cluster (CC) methods at the level of CCSD, CCSD+T(CCSD), CCSD(T), CCSDT-1, and CCSDT-3 are applied to calculations of the dipole moment and polarizability of the CN molecule, ionization potentials and electron affinities of the oxygen and iron atoms and CN molecule, and the energy splitting of the 5D and 5F states of the iron atom. Both UHF and ROHF references are applied. Extended basis sets are used in some comparison of CC data to experiment. All calculated atomic and molecular properties are known as challenging problems, suitable for a careful analysis of the performance of sophisticated versions of the CC approach. Attention is paid to energy terms distinguishing CCSD(T) from CCSD+T(CCSD). We exploit results from various iterative and noniterative high-level CC methods in the assessment of error bars in calculations of atomic and molecular properties. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520121
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  • 165
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    Proton release pathway in bacteriorhodopsin: Molecular dynamics and electrostatic calculations (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 33-56 
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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 use molecular dynamics, electrostatic, and quantumchemical calculations to discuss chromophore and protein structural changes as well as proton transfer pathways in the first half of the bacteriorhodopsin photocycle. A model for the molecular mechanism is presented, which accounts for the complex pH dependence of the proton release and uptake pattern found for the M intermediates. The results suggest that transient transfer of the Schiff base proton to a nearby tightly bound water molecule is the primary step, which is accompanyied by dissipation of free energy to the protein. From there, the energetically most favorable proton transfer is to aspartate D85. Arginine R82 is involved in the protein reorientation switch, which catalyzes the pKa reduction of glutamate E204. This residue is, therefore, identified as extracellular proton release group whose acid base equilibrium regulates the pH-dependent splitting of the photocycle. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520705
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    Conformational analyses of the polymorphism of triglycerides (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 57-77 
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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: Triglycerides, the major components of neutral lipids, are important biomaterials, as they take part in the edification of membranes. In this perspective, the consideration of biological membranes at a molecular level requires detailed knowledge of the preferred conformations of the triglycerides in their various polymorphic forms. In this context, we adapted a molecular modeling approach, which allows the simulation the three-dimensional structure of the different polymorphic forms (α, β′, and β) valid for any triglyceride. Their conformational analysis is based on molecular mechanics calculations, as follows: First, a large number of isolated molecular structures were generated in a systematic structuretree analysis. For their generation, atomic charges within the Mulliken scheme, calculated at the ab initio RHF-LCAO-MO-SCF level (6-31G), were considered. The lowest-energy conformers were, next, correlated with experimental data (NMR, powder X-ray diffraction) in order to select α, β′, or β structures. Then, in a second step, these selected conformers were assembled, in head-to-tail dimers in order to form a monolayer. For this step, the use of potential-derived atomic charges is known to be more suitable. In this study, we consider triglycerides derived from the predominant fatty acids, i.e., stearic, elaidic, and oleic acids. © 1994 John Wiley & Sons, Inc.
    Additional Material: 12 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520706
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    Ab initioSCF investigation of the intramolecular hydrogen bonding in ∊-aminohexanoic acid (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 79-93 
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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 RHF results (geometry data and potential barriers) are reported for the 14 symmetry unique local minima in the potential energy surface of ∊-aminohexanoic acid, which contain an intramolecular N⃛H—O hydrogen bond. Comparison of characteristic data with those of the homologs with fewer carbon atoms shows that δ-aminopentanoic acid forms the most stable hydrogen bonds. In contrast to these homologs, the —COOH group is not limited to anti-periplanar orientation in the H-bonded conformers of ∊-aminohexanoic acid: In four such conformers, it occurs in syn-clinal orientation. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520707
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    Molecular dynamics simulation of crystal water with X-ray constraints (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 109-116 
    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 water in macromolecular crystals is approached with a restrained molecular dynamics method that makes use of X-ray diffraction data, without the need of thermal B factors for the solvent. This method, called here solute-grid-restrained molecular dynamics (SGRMD), is applied to a test case of a simulated crystal of erythrol. The results are quite satisfactory, and it is concluded that the method can be useful to study real macromolecular crystals. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520709
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    Computational studies of the structures and properties of potential antimalarial compounds based on the 1,2,4-trioxane ring structure. I. Artemisinin-like molecules (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 117-131 
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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: Artemisinin and related molecules are potential antimalarials that contain the 1,2,4-trioxane ring system. Several new derivatives have been synthesized and tested in Geneva, and this article presents the results of a systematic study of the structure of these molecules, both by the semiempirical PM3 method and using ab initio SCF methods. The results highlight the feasibility of full optimizations with 3-21G and 6-31G* basis sets for these large molecules. Molecular electrostatic potential (MEP) maps are evaluated and used in an attempt to identify the key features of the molecules that are necessary for their activity. There is good agreement between the PM3 and ab initio maps as to the qualitative predictions. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520710
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    Convergence of a sequence of lower bounds for 〈1/r〉 for the noble gas, alkali, and alkaline earth atoms (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 227-230 
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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 considers 2 × 2, 3 × 3, 4 × 4, and 5 × 5 Gram determinantal inequalities among 〈rn〉, where r is the distance from the atomic nucleus. The elements of these determinants involve n = -1, 0, 1; n = -1, 0, 1, 2, 3; n = -1, 0, 1, 2, 3, 4, 5; and n = -1, 0, 1, 2, 3, 4, 5, 6, 7. The 2 × 2, 3 × 3, 4 × 4, and 5 × 5 determinantal inequalities are used to obtain lower bound estimates of 〈1/r〉 for atoms of spherically symmetric charge distributions. The 2 × 2, 3 × 3, and 4 × 4 inequalities have been applied to He, Ne, Ar, Kr, Xe; Li, Na, K, Rb; and Be, Mg, Ca, Sr. The 5 × 5 inequality has been applied only to He, Li, and Be. It is found that the lower bound values of 〈1/r〉, for all atoms considered, appear to converge to the quantum mechanical values of Boyd, who calculated them with the Roothaan-Hartree-Fock wavefunctions of Clementi and Roetti. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560520823
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    New approximation to the bound states of schrödinger operators with coulomb interaction (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 241-250 
    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
    Notes: In this work we present a mathematical formulation of the physical fact that the bound states of a quantum system confined into a box Ω (with impenetrable walls) are similar to those of the unconfined system, if the box Ω is sufficiently large, and it is shown how the bound states of atomic and molecular Hamiltonians can be approximated by those of the system confined for a box Ω large enough (Dirichlet eigenproblem in Ω). Thus, a method for computing bound states is obtained which has the advantage of reducing the problem to the case of compact operators. This implies that a broad class of numerical and analytic techniques used for solving the Dirichlet problem, may be applied in full strength to obtain accurate computations of energy levels, wave functions, and other physical properties of interest. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560520825
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    The neglect of diatomic differential overlap (NDDO) fragment self-consistent field method for the treatment of very large covalent systems (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 227-236 
    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 present a semiempirical NDDO procedure, called the fragment SCF (FSCF) method, to treat very large molecules. The covalent system is partitioned into a relatively small subsystem where substantial chemical changes take place and an environment that remains more-or-less unperturbed during the process. We expand the wavefunction on an atomic hybrid basis and perform an SCF procedure for the subsystem in the field of the iteratively determined electronic distribution of the environment. We wrote a program for the IBM RISC/560 computer and did several test calculations for a variety of large classical molecules. Protonation energies, proton transfer potential curves, rotational barriers, atomic net charges, and HOMO and LUMO energies, as computed by the exact version of the NDDO method, are fairly well reproduced by our approximation. Using the FSCF method, we calculated the molecular electrostatic potential on the van der Waals envelopes of the specificity pocket of trypsin and the lysine side chain of the bound substrate and visualised electrostatic complementarity. We developed a novel bulk phase Monte Carlo simulation technique and calculated the energy by the above approximation and applied the method to amorphous silicon (a-Si). Starting from a distorted tetrahedrally bonded random network model of a-Si with 216 atoms, we performed Monte Carlo simulations using the FSCF energy calculation. For the second and subsequent configurations, we exploited the feature of the Metropolis- Teller algorithm, namely, that, to generate a new configuration, we displace only a single atom. Thus the number of integrals to be calculated drastically decreases since only those have to be reevaluated that contain the coordinates of the displaced atom. After equilibration we obtained distribution functions being almost identical to the one corresponding to the distortion free tetrahedrally bonded network. The same technique was applied to liquid chlorosilanes. We found that Si—Cl bonds elongate by 6 to 16 pm while H-Si-Cl and Cl-Si-Cl angles change by 2-4° as compared to the gas phase. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520719
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    Quantitative structure-inhibitory activity relationships of substituted phenols on bacillus subtilis spore germination (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 181-185 
    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: Our semiempirical method of calculating log P, which uses a linear combination of various combinations of descriptors based on the AM1-optimized geometry of the molecule, has been applied to a set of 38 substituted phenols and has been shown to be successful in providing a better quantitative structure-activity relationship (QSAR) than that of the Hansch-type approach in a study of the inhibitory activity of substituted phenols on Bacillus subtilis spore germination. This model shows that the calculated partition coefficient, the geometrical descriptors, and electronic effects are the major factors determining the biological activity. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520714
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    Multicavity SCRF calculation of ion hydration energies (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 339-348 
    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 hydration energies of the proton, hydroxyl ion, and several inorganic ions were calculated using the multicavity self-consistent reaction field (MCa SCRF) method developed for the quantum-mechanical modeling of rotationally or flexible systems in dielectric media. The ionic complexes H3O+(H2O)4, OH-(H2O)4, NH4+(H2O)4, and Hal-(H2O)4, where Hal = F, Cl, or Br, have been studied. Each complex was divided between five spheres, corresponding to the central ion and four water molecules in their first coordination sphere, respectively. Each cavity was surrounded by a polarizable medium with the dielectric permittivity of water at room temperature (80). The ionic hydration energies of ions were divided into specific and nonspecific parts. After accounting for the cavity-formation energy using scaled particle theory, good agreement between the total calculated and experimental hydration energies was obtained for all ions studied. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520834
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    Chiroptical techniques and their relationship to biological molecules, big or small (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 315-338 
    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 ab initio theories of electronic and vibrational circular dichroism are presented in brief. For electronic circular dichroism, emphasis is placed on the derivation of optical rotatory strengths by the perturbative configuration interaction approach as implemented in the program PCI. An application to the chiroptical properties of the disulfide chromophore is described. In the infrared region, the ab initio vibronic coupling theory (VCT) of vibrational circular dichroism (VCD) as implemented in the program VCT90, is presented. The relationship to the ab initio magnetic field perturbation (MFP) formalism and an approximate locally distributed origin-gauge (LDO) model is described. The VCT and MFP formulations are compared in large basis set and electron correlated studies of the model system, NHDT, and the experimentally characterized molecule, 2,3-dideuteriooxirane. The LDO model of VCD is applied, together with NMR and molecular mechanics techniques, to the investigation of the conformations of the anticancer drug, taxol. Coupled oscillator models are introduced. Applications both in the area of electronic and vibrational circular dichroism, especially to the determination of secondary structures of proteins and nucleic acids are remarked upon. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520833
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  • 176
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    The dependence of 10Dq upon the metal-ligand distance, R, for transition-metal complexes. What is its microscopic origin? (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 829-835 
    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: Experimental results on 3d Oh complexes in insulators reveal that 10Dq α R-n, where R is the metal-ligand distance and n is close to five. This strong dependence determines the Huang-Rhys factor, S(A1g), associated to the symmetric A1g mode of the first excited state of complexes like MnX64- and CrX63- (X = halide) and makes it possible to measure R changes down to ∽ 10-3 Å. This work is devoted to understanding, within a molecular orbital framework, the microscopic origin of such a dependence, which is related to the corresponding one displayed by the transferred spin densities fσ, fs, and fπ. The analysis is focused on MnF64-. As a main result, it is shown that though fσ ≫ fs the interaction between d(eg) orbitals and 2s orbitals of F- is not only primarily responsible for the R dependence of 10Dq but also makes a significant contribution to the 10Dq value itself. The present work thus shows that the significant dependence of 10Dq upon R is ultimately related to the strong dependence of fs and the isotropic superhyperfine constant As upon R displayed by the experimental results of several 3d impurities. © John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520411
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    Density functional theory applied to the excited states of coordination compounds (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 867-877 
    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: Coordination compounds are usually symmetrical molecules with degenerate orbitals. Hence, the individual multiplet states arising from open-shell configurations can, in general, not be expressed by a single determinant. We have therefore exploited symmetry to the largest possible extent in order to simplify the relation between the multiplet splitting and single-determinant energies and thus developed a new method based on vector coupling to keep the computational effort to a minimum. A system of computer programs working on both mainframe and personal computers has been developed, carrying out for any desired point group the required group theoretical manipulations. The description of the method is illustrated by considering three practical examples. © 1994 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520414
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    Influence of rotation on multiphoton processes in HF (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 173-180 
    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 contribution we are concerned with the role of rotational motion in multiphoton processes induced by a laser field of high intensity. We use the pseudospectral split operator method for the propagation of the quantum wavefunction. The rotation is treated by decomposition of the HF wavefunction in its angular momentum components. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520818
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  • 179
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    The coupled cluster theory of quantum lattice systems (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 155-172 
    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 coupled cluster method is widely recognized nowadays as providing an ab initio method of great versatility, power, and accuracy for handling in a fully microscopic and systematic way the correlations between particles in quantum many-body systems. The number of successful applications made to date within both chemistry and physics is impressive. In this article we review our recent extensions of the method which now provide a unifying framework for also dealing with strongly interacting infinite quantum lattice systems described by a Hamiltonian. Such systems include both spin-lattice models (such as the anisotropic Heisenberg or XXZ model) exhibiting interesting magnetic properties, and electron lattice models (such as the tJ and Hubbard models), where the spins or fermions are localized on the sites of a regular lattice; as well as lattice gauge theories [such as the Abelian U(1) model of quantum electrodynamics and non-Abelian SU(n) models]. Illustrative results are given for both the XXZ spin lattice model and U(1) lattice gauge theory. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520817
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    Ab initio investigation of the static polarizability of planar and twisted infinite polythiophene chains (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 451-467 
    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 we investigate the electronic structure and the static longitudinal polarizability of regular finite and infinite chains of polythiophene at the ab Initio Hartree-Fock level. The effects of the inclusion of polarization functions in the basis set and the influence of introducing a torsional twist between adjacent rings are considered. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520842
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    The relation between magnetism and electronic transport properties in strongly correlated electron liquids, including high tc materials (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 421-432 
    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
    Notes: Liquid metallic caesium, taken up the liquid-vapor coexistence curve towards the critical point, exhibits a crossover from Pauli spin paramagnetism near freezing to Curie-like behavior near criticality. This transition is discussed in terms of conventional Fermi liquid theory at low temperatures and heavy Fermion behavior on approaching the critical region. The maximum in the magnetic susceptibility permits an estimate of the discontinuity q in the momentum distribution at the corresponding density, and this has recently been checked independently using NMR data. An argument is presented, via q, which links a nonequilibrium transport property, namely, electronic conductivity, to a thermodynamic quantity, the magnetic susceptibility. With the above as background, a search has been made for related correlations in the normal state of the high Tc superconducting copper oxides. Using again Fermi liquid theory (now two-dimensional), it is first argued that there should be an intimate correlation between nuclear spin-lattice relaxation time T1 and electrical resistivity R. This is borne out, at least partially, by available experiments. In the same context, the antiferromagnetic susceptibility χ(Q), with Q the antiferromagnetic wave number, is linked with T1 and R. Finally some brief comments are made on the interpretation of Hall and thermopower measurements. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520840
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    Quantum size effects in hexagonal aluminum films (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 675-686 
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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: The work functions and surface energies of Al(111) films ranging from one to seven layers thick have been calculated using the linear combinations of Gaussian type orbitals-fitting function (LCGTO-FF) technique, as implemented in the program package FILMS, an all-electron full-potential electronic structure method. Both quantities exhibit significant quantum size effect (QSE), in basic agreement with three previous investigations using more approximate techniques. However, there are significant quantitative differences among the four sets of results. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560520860
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    1994 Sanibel symposia list of participants (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 695-710 
    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.560520862
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    Companions in the search (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994), S. 739-770 
    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.560490515
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  • 185
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    Electronic structure of DNA dimer units, d(AG) · d, (CT), d(TG) · d(CA), · d(GT), and d(GA), in A and B conformations by DV-Xα cluster calculations (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994), S. 849-875 
    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 d(AG) · d(CT), d(TG) · d(CA), d(AC) · d(GT), and d(TC) · d(GA), which are stacked base pairs in the DNA double helix, are elucidated for A and B conformations in detail by DV-Xα cluster calculations. By using the S̃r values of the O2 (and O3) of each phosphate in the clusters together with those calculated in previous articles, it becomes possible to treat chemical reactivities of phosphates as recognition sites for all DNA fragments. Contour maps of the wave function of the HOMO and LUMO for bases differ subtly among the clusters and show the various fields around the P ion induced by the respective stacking constructed from four kinds of bases. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560490608
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  • 186
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    Origin of steric hindrance in ethane (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 50 (1994), S. 109-112 
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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: Steric hindrance has been regarded as a result of nonbonding atomic repulsion and measured in terms of empirically obtained van der Waals radii. The authors sought the cause of steric hindrance using the partial derivatives of the energy-components with respect to a nuclear coordinate. The results show that electrostatic interactions do not produce steric hindrance but the restriction on electron-movement does. Namely, the kinetic energy pressure is the first cause of steric hindrance. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560500204
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    Numerical computation of bounded states for schröudinger operators (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 50 (1994), S. 113-134 
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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: A method developed previously for computing eigenfunctions of one-dimensional Schrödinger operators is extended to Schrödinger operators in L2(R3N). It is known that in many cases these operators have not a compact resolvent; therefore, the convergence in L2(R3N) of the more used methods for computing the eigenfunctions is not guaranteed. The idea of the present method consists of replacing the eigenvalue problem in L2(R3N) by one corresponding to the system confined into a box Ω with impenetrable walls [Dirichlet problem in L2(Ω)]. It is shown that the eigenfunctions of the unbounded system can be approximated by those of the confined system when the box Ω is expanded. On the other hand, it is proved that the Schrödinger operator associated to the confined system has a compact resolvent and its corresponding sesquilinear form is bounded and elliptic in the Sobolev space W2,10(Ω). These properties guarantee the convergence in L2(Ω) of the standard methods to solve the Dirichlet problem: the Ritz method as well as the finite-element and finite-difference methods. Therefore, the eigenfuncions of the unbounded system can be approximated in L2(R3N) by means of the numerical solutions of the Dirichlet problem in L2(Ω) with sufficiently large Ω. This property guarantees the accurate computation of the true expectation values. © 1994 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560500205
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    Multiple solutions of the single-reference coupled-cluster equations. I. H4 model revisited (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 50 (1994), S. 353-367 
    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: Single-reference coupled-cluster methods corresponding to various approximate forms of the cluster operator including up to four-electron operators are applied to the simple H4 model system with the aim of numerically studying the attainability and properties of multiple solutions of the systems of nonlinear equations for the cluster amplitudes. Various solutions have been obtained for the excited states 21 A1 and 51 A1. It is documented that there exist nonphysical nonstandard solutions that yield energies very close to the physical ones. A simple way of selecting the physically meaningful solutions is proposed. It is demonstrated that the attainability of nonstandard solutions describing a state of H4 within the framework of a given SE-CC method strongly depends on the cluster structure of that state. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560500504
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    Masthead (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 50 (1994) 
    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.560500601
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  • 190
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    The relative stability of the tautomers of α-Hydroxytetronic acid (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 50 (1994), S. 385-394 
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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 relative stability of the four tautomeric forms of α-hydroxytetronic acid was calculated with full geometry optimization at the STO-3G, 3-21G, 6-31G*, and 6-31G** SCF levels. Correlation effects were estimated using the MP2 method. Intramolecular hydrogen bonds are found to be of primary importance for the relative stability of the various tautomers, and the same tautomer that in the case of L-ascorbic acid is experimentally observed in the crystal as well as in solution is found to be the most stable one, if polarization functions on the hydrogen atoms are taken into account. It is concluded that even in the gas phase this tautomer predominates in α-hydroxytetronic acid as well as in L-ascorbic acid. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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    A theoretical investigation of some novel pilocarpine prodrugs (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 35-51 
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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: A new class of pilocarpine double prodrugs of the bispilocarpic acid diester type has been investigated. Molecular orbital and molecular mechanics calculations have been done to obtain information about the conformational preferences and general physicochemical properties. Geometries of the structures were obtained with the force field implemented in the CHEM-X program and using the semiempirical quantum chemical program AMPAC and the AM1 method. A correlation between the van der Waals volume, van der Waals area, and log P of the bispilocarpic acid diester structures is observed. The structures of these biscompounds are compared with the structures of the corresponding monopilocarpic acid diesters. Electrostatic and electronic properties of the compounds will be discussed in the context of the interaction between the prodrugs and the hydrolyzing esterase enzymes. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560510106
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  • 192
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    Electronic Resource
    Erratum (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 53-55 
    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
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560510107
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  • 193
    Electronic Resource
    Electronic Resource
    Path integral approach to correlation energy (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 265-283 
    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 Feynman path integral method is applied to the many-electron problem of quantum chemistry. We begin with investigating the partition function of the system in question; then, “a classical path of electron” that corresponds to the Hartree-Fock approximation is obtained by minimizing the thermodynamic potential of the system with respect to the electron coordinate. The next-order approximation is obtained by evaluating the deviation from this classical path, which is approximately written by an easily integrable Gaussian integral. The result is expected to be the random-phase approximation. As numerical examples, the hydrogen molecule and butadiene are treated. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560510503
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  • 194
    Electronic Resource
    Electronic Resource
    Linear response calculation of potential energy curves of BH (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 307-312 
    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 multiconfiguration time-dependent Hartree-Fock (MC TDHF) approximation is applied to study the excited states of the BH molecule. The potential energy curves and spectroscopic properties of the excited states are analyzed. The MC TDHF results are compared to similar MC SCF calculations for individual excited states. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560510506
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  • 195
    Electronic Resource
    Electronic Resource
    On exact calculation of response properties of oscillators in static electric field: A Fourier grid Hamiltonian approach. I. One-dimensional systems (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 293-305 
    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 Fourier grid Hamiltonian method is used to calculate the response properties of different types of 1-d (one-dimensional) quantum oscillators in a uniform static electric field. The calculations are potentially exact. Excepting the harmonic oscillator, the other model oscillators studied are seen to possess nonlinear polarizabilities. In general, the polarizabilities are not monotonic functions of appropriate vibrational quantum numbers. The exact nature of this vibrational-state dependence of polarizabilities is shown to depend on the type of mechanical anharmonicity in which the nuclei move and the nature of electrical anharmonicity characterizing the field-oscillator coupling. The large vibrational contribution to nonlinear polarizabilities often predicted for real diatomics could therefore originate from the mechanical and electrical anharmonicities of the potential in which the nuclei move when placed in a static electric field. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560510505
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  • 196
    Electronic Resource
    Electronic Resource
    Theoretical study of structure and basicity of some alkali metal oxides, hydroxides, and amides (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 313-318 
    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 (TZV*, SBK*, and 3-21G* or 6-31G* basis sets) calculations were performed to predict the geometries and gas-phase proton affinities of Li2O, LiOH, LiNH2, Na2O, NaOH, NaNH2, K2O, KOH, and KNH2. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560510507
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  • 197
    Electronic Resource
    Electronic Resource
    Electron crystallization in two dimensions (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 329-333 
    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 ground state of the 2D electron crystal is investigated using a localized representation for the electrons. Assuming a neutralizing background, calculation for a nonmagnetic electron crystal is performed. The areal electron densities corresponding to the crystallization for different rs values are computed and these are compared with the available experimental areal densities. An upper limit for the obtainable areal density has been predicted from our results. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560510509
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  • 198
    Electronic Resource
    Electronic Resource
    Incidence of the muffin-tin approximation on the electronic structure of large clusters calculated by the MS-LSD method: The typical case of C60 (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 319-328 
    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 MS-LSD method remains a method of interest when rapidity and small computer resources are required; its main drawback is some lack of accuracy, mainly due to the muffin-tin distribution of the potential. In the case of large clusters or molecules, the use of an empty sphere to fill, in part, the large intersphere region can improve greatly the results. Calculations bearing on C60 has been undertaken to underline this trend, because, on the one hand, the fullerenes exhibit a remarkable possibility to fit a large empty sphere in the center of the cluster and, on the other hand, numerous accurate calculations have already been published, allowing quantitative comparison with our results. Our calculations suggest that in case of added empty sphere the results compare well with the results of more accurate calculations. The calculated electron affinity for C60 and C60- are in reasonable agreement with experimental values, but the stability of C602- in gas phase is not found. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560510508
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  • 199
    Electronic Resource
    Electronic Resource
    Some convergence aspects of the one-center expansion methods (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 345-356 
    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: Among the methods that may be used to carry out multicenter integrals over STOS, the one-center two-range expansion is probably the oldest one. However, the convergence of the leading series is generally slow and, hence, time-consuming. Therefore, it was the aim of the present work to show that the so-called nonlinear sequence transformations may be of substantial help for improving the rate of convergence of such series. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560510603
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  • 200
    Electronic Resource
    Electronic Resource
    Self-consistent approximate solution of the second-order contracted Schröudinger equation (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 369-388 
    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: The general theoretical background for solving approximately the contracted Schrödinger equation (CSchE) in a self-consistent (SC) way has recently been proposed [F. Colmenero and C. Valdemoro, Phys. Rev. A 47, 979 (1993)]. Here, a spin-free procedure is developed and the convergence of the SC iterative process is analyzed using as test cases the beryllium atom and four isoelectronic ions in their ground states. Damping and extrapolation procedures are employed to improve and accelerate the convergence. The results obtained are in very close agreement with those obtained by means of the full configuration-interaction (FCI) method. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560510605
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