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  • 1990-1994  (394)
  • 1920-1924
  • 1890-1899
  • 1991  (394)
  • Computational Chemistry and Molecular Modeling  (394)
  • 1
    Electronic Resource
    Electronic Resource
    Point group symmetry and cartesian force constant redundancy (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 19-29 
    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 procedure for identifying redundancy in the Cartesian force constant matrix is described, and a prescription is given for generating the entire matrix of second derivatives from the minimal set of information. A proof is supplied which demonstrates that the number of nonredundant rows corresponding to a symmetry unique atom is necessarily less than three if the atom is invariant with respect to a symmetry operation of the point group other than the identity or inversion. Furthermore, only one row is required if the atom lies on a threefold or higher-order rotation axis. An application of the procedure to the evaluation of harmonic force constants by numerical differentiation of gradient vectors is briefly described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390105
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  • 2
    Electronic Resource
    Electronic Resource
    An intermediate neglect of differential overlap model for second-row transition metal species (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 31-45 
    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 intermediate neglect of differential overlap (INDO) model for elements of the second transition series is described. Values of exponents for the radial portion of the Slater basis atomic orbitals, the orbital ionization energies, and the beta (or bonding) parameters for these elements are reported. Use of the model to investigate equilibrium geometries, relative energy ordering of geometric isomers, spectroscopic transition energies, energy ordering of state wave functions of different symmetry, trends in dipole moments, and equilibrium stretching frequencies is reported. The results indicate that the INDO method is capable of yielding quality results for species containing atoms of the second transition series.
    Additional Material: 11 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390106
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  • 3
    Electronic Resource
    Electronic Resource
    Improved quadrature methods for three-center nuclear attraction integrals with exponential-type basis functions (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 625-645 
    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 numerical properties of a two-dimensional integral representation [J. Grotendorst and E.O. Steinborn, Phys. Rev. A 38, 3857 (1988)] of the three-center nuclear attraction integral with a special class of exponential-type orbitals (ETO'S), the B functions [E. Filter and E.O. Steinborn, Phys. Rev. A 18, 1 (1978)] are examined. B functions span the space of ETO'S. The commonly occurring ETO'S can be expressed in terms of simple finite sums of B functions. Hence, molecular integrals for other ETO'S, like the more common Slater-type orbitals, may be found as finite linear combinations of integrals with B functions. The main advantage of B functions is the simplicity of their Fourier transform that makes the derivation of relatively simple general formulas for molecular integrals with the Fourier transform method possible. The integrand of the integral representation mentioned above shows sharp peaks causing, in the case of highly asymmetric charge distributions, slow convergence of the quadrature method used by Grotendorst and Steinborn. New quadrature schemes are presented that use quadrature rules based on Möbius transformations. These rules are well suited for the numerical quadrature of functions that possess a sharp peak at or near a single boundary of integration [H.H.H. Homeier and E.O. Steinborn, J. Comput. Phys., 87, 61 (1990)]. Numerical results are presented that illustrate the fact that convergence of the new quadrature schemes is about a factor two faster in case of highly asymmetric charge distributions.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390409
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  • 4
    Electronic Resource
    Electronic Resource
    Single-excitations-adapted molecular orbitals for a simplified description of electronic excited states (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 681-688 
    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 orbital transformation that minimizes the sum of the squares of the off-diagonal Hamiltonian elements between the singly excited configurations is described. The resulting single-excitations-adapted molecular orbitals (SEAMOS) are found to be very suitable for the description of electronic excited states. The test calculations on the singlet and triplet excited states of the N2, CO, and H2CO molecules are presented.
    Additional Material: 12 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390505
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  • 5
    Electronic Resource
    Electronic Resource
    Energy deposition mechanisms and biochemical aspects of DNA strand breaks by ionizing radiation (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 709-727 
    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 model based on physical, chemical, and biochemical mechanisms has been presented to evaluate the yields of DNA strand breaks (single and double) as a function of linear energy transfer (LET) or -dE/dx. Energetic heavy charged particles are considered explicitly to provide a general theory for low- as well as for high-LET radiation. There are three main features of the calculation: (a) track structure considerations for the energy deposition pattern, (b) three-dimensional structure of DNA molecules to provide information on the exact location of damage, and (c) a Monte-Carlo scheme to simulate the diffusion processes of water radicals. To avoid the complexities of a cellular medium, an aqueous solution of DNA is considered in the calculation. When the results of the calculations are compared with experimental measurements of the yields of strand breaks in mammalian DNA (exposed in a cellular complex), reasonable agreement is obtained. However, only those experimental data have been compared where there were no enzyme repair processes. The method of calculation has also been extended to study breaks in higher-order structures of DNA molecules such as chromatin. Specific limitations of the present model have been pointed out for making further improvements.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390508
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  • 6
    Electronic Resource
    Electronic Resource
    Electronic aspects of LADH catalytic mechanismPaper presented at 29th Sanibel Symposia, 1989. (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 767-786 
    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 aspects of the catalytic mechanism of liver alcohol dehydrogenase (LADH) are studied with the help of ab initio analytical gradient SCF MO methods. Three points are considered: (i) role of the catalytic zinc; (ii) geometry and electronic structure of the transition state for the hydride transfer reactions; and (iii) factors affecting the energy gap for the hydride transfer step, namely, substrate binding to zinc, reaction field, and serine 48 effects on the potential energy profile. The coordination sphere of the catalytic zinc has been modeled with an ammonia molecule and two SH- groups; complexes with CH3O-, CH3OH, and CH2O have been studied; a (6, 2, 2, 2, 1/6, 2, 1/3, 2) basis set has been used for Zn++; a (5, 2, 1, 1/3, 2) was used for oxygen, carbon, and sulfur; and a (3, 1) was used for hydrogen atoms. The hydride step was studied with two model systems: pyridinium cation/1,4-dihydropyridine coupled to the CH3O-/CH2O reaction, and cyclopropenyl cation/cyclopropene coupled to the CH3O-/CH2O system. For the latter, the role of Ser48 has been studied at the supermolecule level. The calculation on the hydride transfer step has been done at a 4-31G basis set level. The results obtained shed new light on the sources of catalytic activity of liver alcohol dehydrogenases.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390603
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  • 7
    Electronic Resource
    Electronic Resource
    Theoretical treatment of chemisorption using an Ab initio SCF Green-matrix formalism (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 839-849 
    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 treatment of chemisorption that uses the Green matrix of the surface and the admolecule, as well as a cluster calculation of a small surface cluster. Since full HF-SCF-band structures with nonlocal exchange are available now for larger systems for a couple of years, it is possible to treat the substrate surface and the admolecule on equal footing. This offers a natural way to solve the embedding problem. We have applied the formalism to the adsorption of H2 on beryllium and show that in contrast to cluster calculations there appears a binding, which is experimentally verified.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390608
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  • 8
    Electronic Resource
    Electronic Resource
    A study on the electronic spectra of vinylpyridines and 1,2-(dipyridyl)ethylenes. Molecular orbital calculations (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 211-226 
    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 absorption spectra of 2-, 3-, and 4-vinylpyridines and 1,2-(2,3-dipyridyl), 1,2-(2,4-dipyridyl), 1,2-(3,4-dipyridyl), and 1,2-(4,4-dipyridyl) ethylenes have been investigated in polar and nonpolar solvents. A correlation has been made between the geometry of the molecule and the observed spectrum. Molecular orbital calculations have been carried out using the INDO/S—CI procedure and a limited geometry optimization. The solvent effect at the MO level has been calculated. MO calculations predicted the existence of nπ* transitions that were not observed experimentally. The wave functions of the different CI states were calculated. The experimental transition energy as well as oscillator strength corresponded satisfactorily with the calculated ones. The observed transitions were assigned according to the results of MO calculations.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390210
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  • 9
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390301
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  • 10
    Electronic Resource
    Electronic Resource
    The discovery of the chemical evolution of singlet oxygen. Some current chemical, photochemical, and biological applications (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 251-267 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: From the speculations of G. N. Lewis in 1916, [J. Am. Chem. Soc. 38, 762 (1916)], the spectral predictions of R.S. Mulliken [Nature 122, 505 (1928)], and the quantum mechanical treatment by E. Hückel [Z. Phys. 60, 423 (1930)], the three lowest states of molecular oxygen (3Σg-, 1Δg, and 1Σg+) remained spectroscopic elusives until Gerhard and Lisa Herzberg [G. Herzberg, Nature 133, 759 (1934); L. Herzberg and G. Herzberg, Astrophys. J. 105, 353 (1947); G. Herzberg and L. Herzberg, Astrophys. J. 108, 167 (1948)], precisely defined them by observed infared transitions. The excited singlets remained of interest mainly to atmospheric spectroscopists and astrophysicists, and research on these species was scarce. The discovery in 1963 by A.U. Khan and M. Kasha [J. Chem. Phys. 39, 2105 (1963)] of the simple chemical production of singlet molecular oxygens by the aqueous reaction of hydrogen peroxide and hypochlorite released an explosion of research on the neglected species. Fifteen research symposia and research treatises confirm the broad range of chemical activities of singlet oxygen. The extension to biological systems is now proceeding, with surprising evidence of involvement of natural processes, including the action of singlet oxygen in white blood cell phagocytosis.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390305
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  • 11
    Electronic Resource
    Electronic Resource
    Polarization propagator calculation of spectroscopic properties of molecules (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 371-386 
    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 propose 10 desirable features or criteria for general purpose methods to be applied to the calculation of a range of spectroscopic properties. We discuss the second-order polarization propagator approximation (SOPPA) in light of these criteria by giving the actual computational expression used as well as a few numerical examples taken from the theory of NMR spectra (magnetic shieldings and spin-spin coupling constants). We demonstrate that SOPPA comes close to fulfilling these criteria.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390314
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  • 12
    Electronic Resource
    Electronic Resource
    High-resolution infrared analysis of the ν17 band of pyridine (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 423-436 
    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 for analyzing asymmetric top rovibrational bands displaying both blended and resolved features is described. The two-phase computational procedure uses a modified version of the asymmetric rotor-band contour program FASTPLOT to generate a preliminary set of upperstate spectroscopic constants. The parameters are subsequently refined by employing the assigned line-fitting formalism of the ASYROT program using both resolved and blended features. The technique is detailed in a comprehensive analysis of the ν17 band of pyridine. Inclusion of quartic centrifugal distortion constants was found to satisfactorily model a high-resolution (0.004 cm-1) spectrum of this band, yielding a standard deviation of 0.00137 cm-1. The variation in the rotational parameters with vibrational quantum number is examined in terms of possible weak rovibrational perturbations to the ν17 state. An ab initio calculation of the ν17/ν27 Coriolis coupling constant indicates the observed results are consistent with the interaction of these two vibrational states.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390318
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  • 13
    Electronic Resource
    Electronic Resource
    Announcement (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 521-521 
    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.560390324
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  • 14
    Electronic Resource
    Electronic Resource
    The system of harmonically interacting particles: An exact solution of the quantum-mechanical problem (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 173-181 
    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 original procedure has been developed to determine the eigenvalues and the eigenfunctions of quantum-mechanical many-body systems with a harmonic oscillator interaction. Exact solutions in the explicit form have been obtained for the case of systems containing three groups of identical particles. For the system containing two groups of identical particles, a solution in the adiabatic approximation has been obtained and compared with the exact one.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390207
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  • 15
    Electronic Resource
    Electronic Resource
    Fourth international conference on mathematical and computational chemistry (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 229-229 
    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.560390212
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  • 16
    Electronic Resource
    Electronic Resource
    Professor Michael Kasha (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 233-233 
    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.560390303
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  • 17
    Electronic Resource
    Electronic Resource
    Quantum chemical calculations on buckminsterfullerene and related structures. II. The electronic structure and spectra of some Cn and CnCa2+ cages (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 331-344 
    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: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390311
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  • 18
    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 (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), 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.560390102
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  • 19
    Electronic Resource
    Electronic Resource
    Excited and ionized states of RuO4 and OsO4 studied by SAC and SAC-CI theories (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 93-113 
    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 excitation and ionization spectra of RuO4 and OsO4 are studied theoretically by the symmetry-adapted cluster (SAC) and SAC-CI theories. This is the attempt to assign whole of the spectra by ab initio calculations including electron correlations. In the ground state, electron correlations work to reduce the polarity of the M-O bond overestimated in the Hartree-Fock calculation. The Os-O bond is stronger than is the Ru-O bond, which is reflected in the differences of the excitation and ionization spectra of RuO4 and OsO4. The excitation energies of the experimental spectra are well reproduced by the SAC-CI theory, though the calculated intensities of some peaks are very small in comparison with the experiments. The outer-valence ionization spectra calculated by the SAC-CI theory agree well with the experimental photoelectron spectra. Some shake-up peaks that are accompanied with an electron-transfers from oxygen to metal are also calculated.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390110
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  • 20
    Electronic Resource
    Electronic Resource
    A comment on classical rainbow angles for atom-atom scattering (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 159-162 
    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 dependence of the rainbow angle on the depth of the potential well, the equilibrium distance, andthe force constant of the potential are discussed for several potential functions.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390205
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  • 21
    Electronic Resource
    Electronic Resource
    A general treatment of vibration-rotation coordinates for triatomic molecules (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 183-196 
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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 exact, within the Born-Oppenheimer approximation, body-fixed Hamiltonian for the nuclear motions of a triatomic system is presented. This Hamiltonian is expressed in terms of two arbitrarily defined internal distances and the angle between them. The body-fixed axis system is related to these coordinates in a general fashion. Problems with singularities and the domain of the Hamiltonian are discussed using specific examples of axis embedding. A number of commonly used coordinate systems including Jacobi, bond-length-bond-angle, and Radau coordinates are special cases of this Hamiltonian. Sample calculations on the H2S molecule are presented using all these and other coordinate systems. The possibility of using this Hamiltonian for reactive scattering calculations is also discussed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390208
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  • 22
    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 (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), 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.560400102
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  • 23
    Electronic Resource
    Electronic Resource
    Quantum rigid dipole in a permanent electric field. I. Rigorous treatment (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 33-53 
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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 behavior of a quantum rigid and pointlike dipole in a permanent electric field is under study. A dependence of a number of librational energy levels on the strength of the electric field is investigated on the basis of some rigorous results for the appropriate normal Jacobian matrices.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400106
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  • 24
    Electronic Resource
    Electronic Resource
    A BSSE-free SCF algorithm for intermolecular interactionsSupported in part by the Hungarian Research Fund (OTKA No. 785). (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 139-148 
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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 very simple modification of the usual (∼N4) SCF procedure is proposed, permitting the exclusion of basis set superposition errors (BSSE) in problems of intermolecular interactions. No a posteriori corrections are required. The results of this “CHA/F method” are numerically close to those of the Boys-Bernardi correction scheme but are free from the “overcompensation” characteristic of the latter at smaller distances.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400112
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  • 25
    Electronic Resource
    Electronic Resource
    Symmetry adapted formulation of the generalized Brillouin theorem (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 243-264 
    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 singly excited functions satisfying Brillouin theorem are expressed as linear combinations of configuration-state functions for any spin and spatial symmetries (atomic or molecular) and for any reference wave function. The generality of the formulation is ensured by the use of the irreducible tensor method that can be adapted to any symmetry point group of interest. The expansion coefficients are simply written as products of fractional parentage coefficients, spin- and orbit-recoupling coefficients, and phase factors. The formalism is illustrated for some atomic (Kh) and molecular (C∞v, C3v, and Td) configurations. Group theoretical techniques are also used to correlate the Brillouin conditions within a chain of groups.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400207
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  • 26
    Electronic Resource
    Electronic Resource
    Quantum-Chemical modeling of catecholamine storage including continuum solvent effects (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 299-304 
    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 model for catecholamine storage in vesicles is analyzed within the SCRF-CNDO/2 approach including continuum solvent effects. The model considers the approach of cationic norepinephrine (NE) to a positively charged guanidinium moiety. Ion-pair formation is found for the whole range of dielectric constants. Even though stable states of H-bonded partners are found for large dielectric constants, this process is ruled out to occur because it involves too high energies. It appears that the medium's polarity is determinant in lowering the energy barrier between the ion-pair complex and the separated partners. Thus, as the medium dielectric constant increases, the equilibrium between the two states is enhanced.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400303
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    Electronic Resource
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    Announcement (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 519-519 
    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.560390323
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  • 28
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    Electronic Resource
    Dirac-Fock self-consistent field method for closed-shell molecules with kinetic balance and finite nuclear size (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 487-517 
    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 general method of implementing the kinetic balance condition within the Dirac-Fock (DF) self-consistent field (SCF) formalism for closed-shell molecular structure. We review the steps leading to the derivation of DF SCF equations for closed-shell molecules, particularly as formulated by Matsuoka et al. In the present approach, the large component of the molecular spinors are expanded in terms of atomic basis spinors of spherical-type Gaussian functions, with the small component related to the large component by the kinetic balance condition. It is shown that imposing the kinetic balance condition on geometric Gaussian-type basis functions allows us to obtain the Fock matrix elements, involving both the large and the small components, form the standard nonrelativistic Cartesian-type matrix elements. By using properties of orthogonal polynomials, the solid spherical harmonics are expressed in Cartesian form, thus providing a general basis for transformation of one- and two-electron-matrix elements, obtained from a Cartesian Gaussian-type basis, to a spherical Gaussian-type basis. The advantages of using kinetically balanced geometric Gaussian-type basis functions in molecular DF calculations including finite-size nucleus effects are emphasized. For the sake of completeness, we have added in an appendix corrections to the nuclear attraction matrix elements for the finite-size nucleus already derived by Matsuoka.
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    URL: http://dx.doi.org/10.1002/qua.560390322
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  • 29
    Electronic Resource
    Electronic Resource
    Ab initio MRD-CI calculations for breaking a chemical bond in a molecule in a crystal or other solid environment. III. Me2N—NO2 decomposition of dimethylnitramine in a large crystalline environment (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 541-560 
    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: Recently we extended our strategy for MRD-CI (multireference double excitation-configuration interaction) calculations, based on localized/local orbitals and an “effective” CI Hamiltonian, for molecular decompositions of large molecules to breaking a chemical bond in a molecule in a crystalline or other solid environment.Our technique begins with an explicit quantum chemical SCF calculation for a reference molecule surrounded by a number of other molecules in the multipole environment of more distant neighbors. The resulting canonical molecular orbitals are then localized, and the localized occupied and virtual orbitals in the region of interest are included explicitly in the MRD-CI with the remainder of the occupied localized orbitals being folded into an “effective” CI Hamiltonian. The MRD-CI calculations are then carried out for breaking a bond in the reference molecule. This method is completely general in that the space treated explicitly, as well as the surrounding space, may contain voids, defects, deformations, dislocations, impurities, dopants, edges and surfaces, boundaries, etc.Dimethylnitramine is the smallest prototype of the energetic R2N - NO2 nitramines, such as the 6-member ring RDX or the 8-member ring HMX. Decomposition of energetic compounds is initiated in the solid by a breaking of the target bond. Thus, it is crucial to know the difference in energy between breaking a bond in an isolated energetic molecule versus in the molecule in a solid. In the present study, we have carried out MRD-CI calculations for the Me2N - NO2 dissociation of dimethylnitramine in a dimethylnitramine crystal. The cases we investigated were one dimethylnitramine molecule (surrounded by 53 and 685 neighboring dimethylnitramine molecules represented by multipoles), three dimethylnitramine molecules, and three dimethylnitramine molecules (surrounded by 683 neighbors). All multipoles were cumulative atomic multipoles up through quadrupoles. The MRD-CI calculations on dimethylnitramine required large numbers of reference configurations from which were allowed all single and double excitations.
    Additional Material: 4 Ill.
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    Electronic Resource
    Electronic Resource
    Second-order polarization propagator calculations of dynamic dipole polarizabilities and C6 coefficients (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 667-679 
    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 frequency-dependent dipole polarizability, α(E), is calculated using the second-order polarization propagator approximation (SOPPA). We have shown how to express α(E) as a function of E2 and thus obtained a form of α(E) that can be used to compute C6-coefficients without invoking complex arithmetic. For He we find that SOPPA recovers a large fraction of the correlation contribution for all frequencies, whereas for H2 where the correlation contributions are much smaller and also basis set-dependent, we find a less definite trend of SOPPA relative to RPA.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560390504
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  • 31
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    Electronic Resource
    Transition properties from multiple scattering X-Alpha Calculations: A study of NO2 (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 71-91 
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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 usefulness of the MS-Xα method for calculating molecular transition properties is investigated in a study of NO2. Two-dimensional potential surfaces are obtained in C2v symmetry for the X̃2A1/Ã2B2 system. Potential curves that approximately follow the asymmetric stretch coordinate are also presented: On investigation, no symmetry-broken solutions were found. At all nuclear geometries investigated, the muffin-tin sphere radii were chosen by an energy-minimization technique. The inclusion of corrections to the muffin-tin form of the Xα total energy is shown to be essential, if the computed surfaces are to be qualitatively correct. The transition dipole moment connecting the two states is evaluated as a function of nuclear coordinates, using the transition-state approximation. Finally, the radiative decay of a single vibronic level in NO2 is modeled and the relevance to experiment is discussed.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560390109
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    Electronic Resource
    Electronic Resource
    Monohydration selectivity mechanism of alkali cations in the potassium channel of excitable biomembranes (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 131-147 
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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: Nonempirical quantum chemical method Hartree-Fock-Roothan LCAO SCF MO in a two-exponent Dunning basis with the use of an extended set of Gaussian functions by Huzinaga-Dunning with consideration of electron correlation according to the Meller-Plesset theory of excitations of the second order was used to study monohydrates of Li+, Na+, K+, and HCOO- ions. The indicated basis was supplemented with polarization functions of d-type on the O atom and of p-type on the hydrogen atom as well as with diffusion functions of p-type on the oxygen atom. It has been found that binding energies of the water molecule with Li+, Na+ appeared to be higher and with K+ lower than with HCOO- · H2O. Potential curve shapes of K+ + H2O and HCOO- + H2O reactions are shown to be similar. The molecular mechanism of K+ channel selectivity of an excitable membrane is explained on the basis of the obtained calculations.
    Additional Material: 7 Ill.
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    Collision-induced emission of O2(b1Σg+ → a1Δg) in the gas phaseNRCC No. 31208. (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 287-298 
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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: In flow tube studies of the quenching of O2(b1Σg+), broad band emission of O2(b):M collision complexes was found to appear under the discrete rotational lines of the 0-0 band of the b1Σg+ → a1Δg electric quadrupole transition at higher oxygen pressures and on addition of foreign gases. Bimolecular rate constants for the collision-induced emission processes have been derived from the ratio of the intensities of the discrete lines and the continuum as well as from low-resolution measurements of the relative intensities of the b → a and b → X bands as a function of O2 and added gas pressure. They range from ≈10-21 cm3 s-1 for He to ≈4 × 10-19 cm3 s-1 for PCl3 vapor.
    Additional Material: 8 Ill.
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    Electronic Resource
    A realistic model for curve crossing in diatomic molecules (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 523-539 
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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 present a model system for the study of curve-crossing situations in diatomic molecules. All model parameters are determined by the potential energy topology. No coupling functions are fitted. The standard approximation schemes (Born-Oppenheimer approximation, adiabatic approximation, and the generator coordinate approximation) are then applied. The result of these numerical experiments suggest that the generator coordinate approximation is able to remove 80%-90% of the nonadiabatic effect on all levels throughout the crossing region.
    Additional Material: 7 Ill.
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    Electronic Resource
    A partial recurrence relation for reduced class coefficients of the symmetric group (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 593-604 
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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 expression for the product of a single-cycle class [(1)N - P(p)]N and an arbitrary class [(1)l1(2)l … (N)lN]N of the symmetric group has recently been conjectured. This expression involves a sum over a relatively small number of reduced class sums, depending on p indices. A further conjecture is formulated and demonstrated, according to which reduced class coefficients (RCCS) involving cycles whose length is expressed by means of a single index can be related to corresponding coefficients in the product of [(1)N - P+1(p - 1)]N with an arbitrary class sum. Consequently, the problem of evaluating the general class sum product reduces to that of obtaining a relatively small set of fundamental RCCS containing no single-index cycles. The conjectures mentioned can be used to evaluate the product [(1)N - p(p)]N · [(1)N - q(q)]N in terms of fundamental RCCS that can all be obtained from the product [(r)]r · [(r)]r, where r = min(p, q). For the latter product, we use a result due to Boccara.
    Additional Material: 2 Tab.
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    Electronic Resource
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390501
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    Structure reports for 1988. Edited by G. Ferguson and J. Trotter, metals and inorganic compounds, Vol. 55A, Kluwer, Dordrecht, 1989 (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 647-647 
    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.560390410
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  • 38
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    Electronic Resource
    Exciton interactions in the spectrum of a dinaphthonorbornadiene (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 345-352 
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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 near-ultraviolet spectrum of a dinaphthonorbornadiene is reported and is interpreted using simple exciton theory that treats this molecule as a dimer of naphthalene. It shows examples of weak, intermediate, and strong coupling for the interaction of the three observed bands of naphthalene.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560390312
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    Electronic Resource
    The dynamics of equally spaced multilevel model systems (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 387-397 
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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: Coherent dynamics of multilevel systems is of interest for the elucidation of energy disposal and multiphoton chemistry of polyatomic molecules. We compare the analytical solutions for coherent multiphoton excitation of two sparse multilevel model systems: (1) The spin-J system consisting of N = (2J + 1) equally spaced levels with the radiative coupling being determined by the xth component of the angular momentum. (2) The equally coupled N level system. The transition amplitudes for system (1) are always periodic, which is in contrast to the nonperiodic behavior exhibited by system (2) for N 〉 3.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560390315
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    Electronic Resource
    Van der waals modulated spectral intensities: Application to infrared absorption (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 437-447 
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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 formulation is presented of the effects of van der Waals interaction on infrared intensities. The theory takes account of induction and dispersion interactions (including charge interpenetration) and is applicable to fluids of arbitrary density. The transition moments are developed from generalized van der Waals-induced moments, and expressions are obtained for the adsorption coefficient in terms of generalized charge densities and charge-density (hyper)susceptibilities. Explicit expressions are given also of the integrated absorption coefficient in terms of multipoles, and (hyper)polarizabilities and their derivates, and the usefulness of this formulationin interpreting experimental data is illustrated by several examples. The relevance of the induction and dispersion interactions to allowed and to forbidden transitions made allowed is discussed.
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    URL: http://dx.doi.org/10.1002/qua.560390319
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    Interaction between theory and experiment in molecular core electron spectroscopies (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 455-486 
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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 interaction between theory and experiment in the field of molecular core electron spectroscopies is reviewed. Those aspects that distinguish the theoretical descriptions of core and valence electron spectra are analyzed in particular. Differences in the theoretical approaches to atomic and molecular spectra in terms of scattering and many-body theories are commented on. The molecular core electron spectroscopies are analyzed from a common point of view with respect to molecular orbital theory, many-body theory, and the role of localization and local selection rules. A brief analysis is presented for the particularities that enter the calculations of core hole spectra. Solutions are described to computational problems posed by the quasi-bound, highly excited nature of core hole states and by the large electronic relaxation following their creation. Two areas where the interaction between theory and experiment is particularly fruitful are briefly reviewed, namely, the theory of vibronic excitations in core electron spectra and the theory of the core photoelectron chemical shift.
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    URL: http://dx.doi.org/10.1002/qua.560390321
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    Electronic Resource
    Non-local relation between kinetic and exchange energy densities in Hartree-Fock theory (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 585-592 
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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 non-local generalization K(r, r') of the kinetic energy t(r) such that t(r) = ∫K(r, r') dr' is defined using the idempotency property of the Hartree-Fock first-order density matrix. This is, in turn, related by means of an explicit differential equation to the non-local exchange energy density X(r, r'). The relationship is illustrated for a couple of examples: with the Fermi-hole in a uniform electron gas, of importance in the local density version of density functional theory, and with inhomogeneous electron systems.
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    Electronic Resource
    Aromaticity measured by Kekulé structures (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 605-613 
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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 total energies, in the Hückel theory, of a large number of polyhex molecules and some containing a four-membered ring have been calculated and analyzed. The results confirm that within a set of isomers the number of Kekulé structures is the dominant variable. It is proposed that this term should be recognized as the aromatic term. The remaining contributions to the energy can be attributed to local features of the molecule. Comparison with the Hess-Schaad analysis of the same energies indicates that this treatment is simpler, more complete, and closer to the original concept of aromaticity.
    Additional Material: 2 Ill.
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    Electronic Resource
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390101
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    Transferability of the electronic structure characteristics of saturated moleculesThis article was originally presented at the 1989 Sanibel Symposium. (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 11-17 
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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 common quantum mechanical problem for the total class of saturated hydrocarbons has been stated and solved within the framework of the effective Hamiltonian method. A quantum mechanical substantiation of the transferability of the electronic structure characteristics (bond dipole moments, bond energies, and bond force constants) as well as the investigation of the origin of transferability have been considered for the stated class of chemical compounds.
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    Topological analysis of eigenvalues of particle in one- and two-dimensional simple quantal systems: Net sign approach (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), 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: Simple net sign analysis has been carried out for particle in one- and two-dimensional boxes and harmonic oscillators. The conclusion that no simple rule for the ordering of eigenvalues of two-dimensional systems can be drawn is conjectured. Cyclobutadiene, naphthalene, benz-cyclobutadiene, biphenylene, biphenyl, and p-terphenyl are found to behave topologically as particle in either type of potential. Benzene, anthracene, naphthacene, and pentacene are found to behave topologically as particle in a two-dimensional harmonic oscillator. This analysis provides the physical basis for the net sign approach in the signed graph theory.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560390108
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    The rapid estimate of a gauss integral (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 123-130 
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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 propose a fomula that directly gives an estimate of the value of a Gaussian integral through only one multiplication. Using this formula, we may neglect about 60%-80% of integrals in quantum chemical ab initio calculations, without any loss in precision theoretically. Such a large molecule as ATP with 183 STOS using the STO-2G method has been calculated utilizing this technique, and only 31 CPU hours of VAX 11/730 were spent on integrals.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560390202
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    Calculations using a set of evenly spaced S-type gaussian functions (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 163-172 
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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 basis set of evenly spaced S-type Gaussian functions with common exponents is examined. Formulas for common one- and two-electron integrals are derived. Because of thesymmetry of this basis set, a very compact two-electron integral list is produced. The number of two-electron integrals that must be stored is approximately eight times the number of basis functions. Use of this basis set in an SCF calculation is examined. Numerical results show that this approach works well for molecules containing only small atoms such as hydrogen, helium, or lithium, but that the method has problems with the core orbitals of heavier atoms. Procedures for augementing this basis set in calculations involving heavier atoms are examined.
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    URL: http://dx.doi.org/10.1002/qua.560390206
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    Quantum chemistry: Basic aspects, actual trends. Edited by Ramon Carbó, Elsevier, Amsterdam, 1989 (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 227-228 
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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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390211
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  • 50
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    Introduction (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 231-231 
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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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390302
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    Dipole moments, transition moments, oscillator strengths, radiative lifetimes, and overtone intensities for CH and CH+ as computed by quasi-degenerate many-body perturbation theory (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 269-286 
    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 correlated, size-consistent, ab initio effective valence-shell dipole operator (μv) method is used to calculate dipole moments and transition dipole moments of the CH molecule and transition dipole moments of the CH+ ion as a function of internuclear distance. The dipole and transition dipole moments computed here compare well with those of other accurate ab initio methods. The transition dipole moments are then used to calculate oscillator strengths and radiative lifetimes for the A → X and B → A transitions of the CH+ ion and the A → X transition of the CH molecule. Comparisons are made with the best available theoretical and experimental lifetimes. Finally, the CH ground-state dipole moment function is used to evaluate overtone intensities and to examine simple models of the CH overtone intensities in polyatomic molecules.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390306
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    Electronic Resource
    Charge-transfer intensity in complexes with symmetrically equivalent acceptors (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 299-308 
    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: Mulliken's model for the intensity of charge-transfer absorption bands in donor/acceptor complexes is extended to transition-metal compounds. Attention is focused on the analysis of systems containing a central metal ion and symmetrically equivalent π-acceptor ligands. The theory is illustrated for a one-donor/two-acceptor complex in D2d point symmetry. Results are stated for symmetries of commonly occurring transition-metal compounds that display well-documented metal-to-ligand charge-transfer transitions.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560390308
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    A generalization of the method of stimulated emission pumping (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 325-330 
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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: Drawing on the results of an analysis of the nature of the pulse that generates complete transfer of population from one to another level in a system with a discrete spectrum, a generalization of the method of stimulated emission pumping is proposed. It is shown that a small subset of the Fourier components of the optimal pulse will, if their relative amplitudes are the same as in the optimal pulse, generate almost as efficient a population transfer, thereby generating the opportunity to prepare a system in a selected state with a selected population.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560390310
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    Model study of the abrupt excess-energy dependence of radiationless decay in benzene and azabenzenes (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 309-324 
    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: Model studies are reported aimed at accounting for the abrupt dependence of radiationless decay-rate constants on excess energy (known as channel-three decay in the case of S1 benzene) in singlet and triplet manifolds of benzene and azabenzenes. The favored model involves La(ππ*) state, strongly distorted along an out-of-plane coordinate, crossing the ground-state potential at an energy close to the minimum of the lowest excited state. The results are compared with experimental observations on benzene and three azabenzenes. Implications for photochemical reactions are also discussed.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560390309
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    Theory of ultrafast time-resolved absorption spectroscopy (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 353-370 
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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: In this paper, the density matrix formalism has been applied to treat ultrafast time-resolved absorption spectroscopy. We have shown that in the femto-second (fs) pump-probe experiments, the observed time-resolved absorption spectra consist of the contributions from the population (i.e., incoherent contribution) and the coherence (i.e., the phase of the system). The adiabatic approximation has been used to derive the expressions for ultrafast time-resolved spectra. We have also shown that the dynamics of the coherence will result in quantum beat. Numerical calculations have been performed to demonstrate the theoretical results.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560390313
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    Ab initio simulation of benzene Raman intensities (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 411-422 
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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: C6H6 Raman scattering activities calculated from harmonic model ab initio Hartree-Fock 6-311 ++ G(d, p) polarizability derivatives (and harmonic force fields calculated at the same level) accurately simulate experiment (to within 1% for the a1g modes). Accurate predictions are also made for the e2g modes (to within 5% for ν7 and ν9, and more poorly for ν6 and ν8 [in Fermi resonance with ν6 + ν1]) and for the e1g out-of-plane mode, ν10. Only the ν6 in-plane CCC bending mode scattering activity is found to be anomalous. Systematic variation of the basis set indicates that the benzene scattering activities and depolarization ratios are strongly dependent on inclusion of both carbon and hydrogen atom diffuse functions in the basis set. Predictions are also made for 12C6D6 and for unmeasured intensities in 13C6H6. Measurements of a1g mode scattering activities in the latter molecule are predicted to be useful in testing the harmonic Hartree-Fock Raman intensity model.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560390317
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    Normalized irreducible tensorial matrix expansions applied to an effective sp-type Hamiltonian for the PES of water (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 347-360 
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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: Any matrix can be expanded on a basis of SU(2) normalized irreducible tensorial matrices, NITM, defined in terms of 3-j symbols or coupling coefficients of SU(2). The NITM transform under rotations according to Wigner's matrices. If one dimension of an NITM is odd and the other even, the tensor has half-integer rank. A simple NITM basis consists of all NITM having the same numbers of rows and columns as the expanded matrix. A compound NITM basis consists of two or more simple bases, each spanning a corresponding block in the expanded matrix. The choice of NITM basis for expanding an effective Hamiltonian matrix is a crucial step in formulating a model. To illustrate the use of a compound NITM basis, including nonsquare NITM, an effective sp-type overlap-free superposition Hamiltonian is constructed and applied to the photoelectron ionization potential spectrum of water.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400307
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    Further investigation of the spatial generalization of Kato's theorem by a variational density-functional approach (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 409-414 
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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: In a recent work, Csvinszky formulated a variational density-functional approach for the investigation of the spatial generalization of Kato's theorem by March. In the previous work, a 10-electron model system (filled K and L shells) was considered. In the present work, the investigation is extended to two other cases: a 28-electron model system (filled K, L, and M shells) and a 60-electron model system (filled K, L, M, and N shells). As in the previous work, several expressions are adapted for the kinetic-energy functional of the electrons and the intriguing question of identifying the “best” kinetic-energy functional is raised and discussed.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560400312
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    Second-order correlation potential in the Kohn-Sham approximation for atoms (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 421-428 
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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 type of correlation functional derived from the second-order expression for the correlation energy of an atom is proposed. The derived correlation potential contains one free parameter, which is determined by fitting the known pair correlation energy. The calculations with this potential in the Kohn-Sham approximation give rather accurate values for the matrix elements of different operators.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400314
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    Harmonic oscillator tensors. I. The nondegenerate case (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 457-473 
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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: It is shown that the Heisenberg Lie algebra of the nondegenerate harmonic oscillator leads to a basis {J+, J0, J-} of LASU(2). The Hamiltonian of the system is proportional to J0, and the basis elements give rise to irreducible tensors in the associative enveloping algebra of the Heisenberg Lie algebra. The construction of these irreducible tensors is studied with special attention being paid to the case in which they act upon a single vector space spanned by the harmonic oscillator basis functions. A tensor coupling rule is developed, and useful application is made of it in the calculation of general expressions for vibrational operators and their matrix elements. Throughout, the value of the additional algebraic quantum numbers (l, m) is emphasized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400403
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    Phase associated with the single-particle density of many-electron systems (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 501-510 
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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: In excited states of atoms and molecules, as well as in time-dependent situations, the one-electron density no longer suffices to completely characterize the electronic state; in addition, one now requires information about the electronic phase or the current density. We show that, for a stationary electronic state, the continuity equation of quantum fluid dynamics represents a differential equation for the electronic phase, which must be solved subject to certain periodicity conditions. These periodicity conditions arise from the nodal topology of the wave function and give rise to quantized vortices of current. The consequences of writing an electronic “wave function” for a many-electron system directly in terms of the single-particle density and phase have been investigated. We have shown that such a procedure leads to the appearance of an “internal magnetic vector potential.” We also establish the connection between the electronic phase and the geometrical (“Berry”) phase accompanying the adiabatic transport of a quantal system around a closed loop in parameter space. This leads to a generalization of the current density concept and allows us to discuss the geometrical phase in terms of the circulation of this current in parameter space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400406
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    Approximate separation of the hyperradius in the many-particle Schrödinger equation (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 657-666 
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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: For large values of d = 3N, the radial distribution function of an N-particle system is sharply peaked near the hyperradius rm = (d - 2)/2k0, where k0≡(2/E/)1/2. This fact allows an approximate separation of the hyperradius, leading to many-dimensional hydrogenlike radial solutions. Kindred applications to dimensional scaling are also discussed, where d = DN, with D the spatial dimension. For the large D regime, illustrative analytic formulas are obtained giving the energy and effective nuclear charge for the lowest few S states of the helium atom.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560390503
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    Analysis in terms of valence-bond structures of environmental effects on the electronic structure of moleculesA contribution from the “Grup de Química Quàmtica de l'Institut d'Estudis Catalans.” (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 511-525 
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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: Environmental effects on the electronic structure of molecules caused by external perturbations are studied by means of an expansion of molecular orbital wave functions into valence-bond (VB) wave functions. Applications are carried out to the π system of butadiene, hydroxyethylene, acrolein, and carbonyl oxide and also to the full electronic system of water. The external perturbations considered are uniform electric fields, nonuniform electric fields, and reaction fields created by solvents. A different behavior is found between nonpolar and polar species in the presence of solvents. Some consequences on the behavior of molecules under the influence of the different electric fields are discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400407
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    The elements of Flatland: Hartree-Fock atomic ground states in two dimensions for Z = 1-24 (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 527-544 
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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 Hartree-Fock problem in two dimensions (2D) has been solved for 1 ≤ Z ≤ 24 using a Gaussian basis and assuming r-1 Coulomb interactions. The order of occupation of the one-electron states is \documentclass{article}\pagestyle{empty}\begin{document}$$ 1s\, \ll \,2s\, 〈 2p\, 〈 3s\, 〈 3p 〈 4s\mathop 〈 \limits^ \approx \,3d 〈 4p $$\end{document} like in the 3D case. The 1s shell is found to be particularly small and strongly bound, making the 2D hydrogen a “superhalogen” and the 2D He a “superinert gas.” In contrast to 3D, 4s13d2 and 4s23d3 configurations are preferred for the 2D “Sc” and “Cu,” respectively. The six first 2D atoms have stronger and the later ones weaker valence-bonding energies than do their 3D analogs. It is noted that the 2D Dirac energy expression for a hydrogenlike atom for mj = l + 1/2 agrees with the 3D Klein-Gordon one.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400408
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    The electronic structure of parallel β-pleated sheets in proteins: An ab initio computation including electron correlation (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 559-576 
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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 electronic structure of a 2D polyglycine network with a pleated sheet structure has been computed at the Hartree-Fock level and by including electron correlation effects within the second order of many-body perturbation theory (electron polaron model). The influence of the size of the atomic basis set and of the extension of the virtual space has been investigated both for single- and many-particle properties. Comparison with the energy of the corresponding single chains showed that interchain interactions (mainly hydrogen bonding) provide an extra stabilization for the 2D network by 7.4 and 10 kcal/mole per glycine residue at the Hartree-Fock and correlated levels, respectively. The energy dispersions are rather anisotropic for all bands whose widths are about 0.5-1 eV along the polypeptide backbones and 0.1-0.2 eV in the perpendicular direction (hydrogen bonds). The HF value of the fundamental energy gap is reduced by 4 eV to 9.2 eV for electron polarons. The wave functions and interaction integrals obtained can be used to calculate further optical and lattice vibrational properties.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400410
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    Harmonic oscillator tensors in contact transformation theory (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 623-642 
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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 application of contact transformation theory to the perturbed harmonic oscillator is reexamined in the light of the harmonic oscillator tensors previously presented. It is found that the recasting of the formalism of this problem in terms of harmonic oscillator tensors results in great simplifications, most of which stem from the introduction of the additional algebraic quantum numbers (l, m). The order of magnitude of each fragment of the Hamiltonian is easily recognizable, and the diagonal and nondiagonal parts contained therein are readily identifiable. The determination of the contact transformation operator is reduced to a simple formula. First, an analysis is made for a single mode of vibration, and it is subsequently extended to a multimode case. The perturbed diatomic vibrator is presented as an example.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400506
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    Analytic form of Thomas-Fermi-Dirac dielectric function for III-V compound semiconductors (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 695-702 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nonlinear Thomas-Fermi-Dirac equation is solved variationally for positive and negative point charges in various III-V compound semiconductors. The parameters are presented, and the results are compared with those obtained numerically.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400511
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    Masthead (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400601
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    Two-electron repulsion integrals over Gaussian s functions (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 745-752 
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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 present an efficient scheme to evaluate the [0](m) integrals that arise in many ab initio quantum chemical two-electron integral algorithms. The total number of floating-point operations (FLOPS) required by the scheme has been carefully minimized, both for cases where multipole expansions of the integrals are admissable and for cases where this is not so. The algorithm is based on the use of a modified Chebyshev interpolation formula to compute the function exp(-T) and the integral Fm(T) = ∫01u2mexp(-Tu2) du very cheaply.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400604
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    A contracted bromine basis set for use in calculation of molecular energies (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 781-787 
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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 contracted [9s6p2d] basis set derived from Dunning's (14s11p5d) primitive Gaussian set for bromine has been used in ab initio molecular orbital calculations of the dissociation energies of HBr, CH3Br, and Br2, the ionization potentials of Br and HBr, and the electron affinity of Br. The calculated energies are within 0.1 eV of the experimental values. This is similar to the accuracy obtained in a previous study, also using a contracted [9s6p2d] basis set, of the dissociation and ionization energies of the GeHn, AsHn, and SeHn hydrides.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400607
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    Portable tools and applications for parallel computers (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 847-863 
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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 distributed-memory model is adopted for the development of parallel ab initio codes with an emphasis on portability as well as efficiency. A highly portable message-passing toolkit (inspired by the Argonne ACRF PARMACS) is described. Examples and results of its use are presented.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400612
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    Introduction (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. vii 
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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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400703
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    Molecular structure and functionAlso published in Int. J. Quantum Chem. Chem. Symp., 25 (1991). (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 1-8 
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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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400706
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    Papain in aqueous solution and the role of Asp-158 in the mechanism: An Ab InitioSCF + DRF + BEM study (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 49-59 
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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 effects of the solvent on the stability of the zwitterion in the active site of papain is investigated with numerical methods. The solvent is represented by a homogeneous dielectric continuum surrounding a cavity, defined by a fragment of the protein enclosed by a surface obtained following Connolly's method. The discretisized boundary surface is used to solve the Poisson equation in its integral form by means of a numerical approximation based on the boundary element method (BEM), resulting in a set of surface polarization charges. The solvent effect on the proton transfer in papain is studied on the basis of MO-SCF-direct reaction field (DRF) calculations of the energy and charge distribution of the fragment in the field of the surface charges. The role of Asp-158 in the proton transfer in the active site of papain is reevaluated in the presence of the solvent. It is concluded that the effect of the negative charge of Asp-158 is nearly completely screened by the solvent.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400710
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    Electronic factor in biological electron transfer systems. Role of aromatic side groups (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 99-118 
    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 factor for electron transfer (Δ) is calculated in proteins and in model systems using the CNDO/S and ab initio methods. The decrease of |Δ| with distance for oligoglycins in different conformations is compared to the decrease in other oligomers. The rate of an intramolecular ET reaction in azurin from a disulphide bridge to Cu(II) is calculated with satisfactory agreement with the experiments. For a pathway with three aromatic side groups we obtain a slightly larger electronic factor than one without such groups but the latter do not seem to be essential for the ET process in this case. The primary electron transfer step in the bacterial photosynthetic center of Rhodopseudomonas viridis is studied. The calculated |Δ| for a direct electron transfer process P*BChlLBPhL—P+BChlLBPhL- is very small and inconsistent with the high rate measured. The accessory chlorophyll, being almost perpendicular to the special pair and pheophytin chromophores, does not seem to have good bridging properties and a much larger coupling is provided by the Tyr M208 phenol side group. However, this coupling is also too small to explain the rapid primary charge separation. We believe that the energy splitting between the charge separated singlet and triplet states caused by this coupling is essential to prevent wasteful triplet formation.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400714
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    Vibrational modes in the agonist and antagonist action of ligands on the β1-adrenoceptor and some receptor site geometry (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 151-164 
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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 one-dimensional model for the agonist action of phenoxypropanolamine agents on the β1-adrenoceptor can be based on two electronegative receptor sites positioned from known ligand-receptor interactions. One of these sites interacting with the protonated amine moiety of the ligand and associated with the initiation of stimulus action was shown to be consistent with the presence of an anion in a related article. Contraction of the relevant unbound phenoxypropanolamine conformer is required to enhance the charge-charge interaction. The free energy of contraction of the phenoxypropanolamine conformer with consequent movement of the side chain polar moieties to a position more coincident with that of an ethanolamine has been estimated in two parts using minimal basis STO-3G calculations. The unprotonated species was considered adequate for estimating the intrinsic changes in the backbone compression. Movement of the aromatic ring in the one-dimensional axis due to in-plane meta and para hydrogen atom distortion was earlier shown to be consistent with a displacement of 0.1 Å with an enthalpy requirement of 2.2 kcal. For the aliphatic side chain, an STO-3G enthalpy estimate of 4.6 kcal was required for a movement of 1.0 Å in the position of the protonated amine moiety towards the aromatic ring. Changes in vibrational contributions due to the contraction were small, the entropic contribution being 0.15 kcal, giving a free energy of distortion in the aliphatic side chain of 4.7 kcal. The net movement of the protonated amine and its attendant β-hydroxyl is thus some 1.1 Å in the onedimensional axis for an estimated expenditure of 6.8 kcal enthalpy. Since there is an estimated 6-7 kcal enthalpic advantage shown by the side chain's polar interaction in agonist as opposed to antagonist action, this degree of distortion is consistent with the production of a partial agonist. In the dominant axis of the compression model, the phenoxypropanolamine phenyl ring lies some 0.5-0.7 Å below that of the nonarenaline conformer. The net lowering of the amine moiety in this axis would therefore be 1.6-1.8 Å, but for its raising by 1.9 Å due to the presence of the —OCH2 moiety. The estimate for the distortion for each of the receptor polar sites for agonist interaction would be less than 0.15 Å. In addition, there may be a further 1-2 kcal of free energy still available for further ligand distortion due to the potential amplification of the stimulus signal. The energetics of the model are therefore of the right order in estimating the position of polar receptor sites with good accuracy.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400717
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    DNA bending studied by MD and 2D NMR NOESY simulations: Role of the junction sequence between the A/T tracts (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 213-229 
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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 performed all-atom constant temperature (T = 285 K) molecular dynamics (MD) simulations on d(GA4T4C)2 and d(GT4A4C)2 for 200 ps using the NMR-derived structures as the starting points. The major purpose of MD simulation is to search the conformational space so that we can construct an ensemble of conformations that will reproduce the experimentally observed 2D NMR NOESY spectra. Analyses of the ensemble of duplex structures reveal that in both oligomers constituent nucleotides predominantly display BI conformations. A simple two-parameter analysis shows that the nature of the long-range collective bending motion is different in the two duplexes. The conformations obtained by use of molecular dynamics are very similar to each other for the same molecule, the root mean square deviation (RMSD) being 1.6 Å for d(GA4T4C)2 and 1.1 Å for d(GT4A4C)2. We have computed theoretical 2D NOESY spectra for an ensemble of a large library of 1200 structures in the MD trajectory for d(GA4T4C)2. Theoretical MD-derived 2D NOESY spectra, averaged through an automated loop computation procedure over the 1200 timewise additivity NOESY simulation spectra, are compared with the corresponding experimental spectra. The agreement between the theoretical and experimental NOESY spectra is good. The results suggest that there is no longer any need to interpret NMR data on the basis of a “nonexistent” time-average structure and that worthwhile information about the realistic composition of the ensemble of conformations that are present in solution can be obtained by interconnecting MD simulations and NMR data.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400722
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    Empirical methods for computing molecular partition coefficients. I. Upon the need to model the specific hydration of polar groups in fragment-based approaches (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 299-316 
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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 empirical approach for the computation of log P for flexible molecules has been developed. This approach is based upon the use of fragmental parameters for obtaining the free energy of solvation of a given molecular conformation in both water and octan-1-ol. Two parametrization methods have been investigated, and the quality of the fragment parameters obtained assessed by computation of log P values for a number of compounds which can only adopt a single conformation. Comparison of these calculated log P values with experimental measurements revealed that simple empirical models which assume a linear relationship of transfer free energy and fragment solvent accessible area do not adequately represent the interaction of polar fragments with water molecules. In the second parametrization method, therefore, a novel step function was introduced, based upon physical models of the specific hydration of polar fragments able to participate in hydrogen bonding, by water molecules. Fragment parameters derived by the second approach gave excellent agreement between calculated and experimental log P values for rigid molecules containing several classes of functional group.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400727
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    International journal of quantum chemistry - a journal devoted to quantum theory and computations in chemistry, condensed matter physics, and biology. Editorial - program and policies (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. ix 
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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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400802
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    William Nunn Lipscomb, Jr. Curriculum Vitae (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. xxix 
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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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400805
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    1991 Sanibel symposia list of participants (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. xiii 
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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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400804
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    Molecular structure and functionAlso published in Int. J. Quantum Chem. Biol. Symp., 18 (1991). (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 1-8 
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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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400806
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    Renormalized ground states in electron propagator theory (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 35-42 
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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: Electron propagator theory provides a correlated one-electron picture of bonding through accurate calculations of electron binding energies and Feynman-Dyson amplitudes. Reference state averages are improved with certain infinite-order corrections by employing amplitudes from coupled cluster singles and doubles calculations. The results contain all corrections to Koopmans's theorem through third-order and many infinite-order corrections. Illustrative calculations are performed on the ionization energies of H2O, HF, BH, and OH-, and on the electron affinities of CaF+ and CH+.
    Additional Material: 6 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560400808
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    On the solution of coupled-cluster equations in the fully correlated limit of cyclic polyene model (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 9-34 
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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: It is shown that the exact pair-cluster coefficients corresponding to the fully correlated limit of cyclic polyene model satisfy the equations of the approximate coupled-pair theory with quadruples (ACPQ) approach, but do not represent any solution of the standard coupled-cluster method with doubles (CCD) equations. Implications of this result for the performance of various coupled-cluster (CC) approaches, when applied to cyclic polyene model, are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400807
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    Maximum similarity orbitals for analysis of the electronic excited states (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 81-93 
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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: A new theoretical tool for analyzing the excited-state wave functions obtained from separate Hartree-Fock or configuration-interaction calculations on each state is proposed. Isopycnic transformations among the natural spin-orbitals of the ground and excited states yield the maximum similarity spin-orbitals (MSOs). These MSOs, which are a generalization of the method of corresponding spin-orbitals due to Amos and Hall, allow one to identify the initial and final spin-orbitals associated with the electronic excitation. The proposed formalism is equally valid in the cases of either identical or different geometries of the ground and excited states and makes it possible to assess magnitudes of the nuclear and electron relaxations accompanying the excitation. The methodology is illustrated using the example of the ROHF/6-31G** calculations on the keto and zwitterionic forms of the 3-hydroxypyrone molecule in their ground and two lowest-lying triplet excited states.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400811
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    Optimized second-order correlation orbital manifold for single excitations in the coupled-cluster method (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 71-80 
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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 sum of the second- and fourth-order Hylleraas functionals and the Newton-Raphson optimization technique have been used to optimize a manifold of first- and second-order correlation orbitals (FOCOS and SOCOS) for the spin-restricted Hartree-Fock (RHF) wave function. The correlation orbitals are linear combinations of the RHF virtual orbitals. The computational implementation of the new method is discussed and a numerical application to a simple model system is presented to illustrate the capabilities of the proposed methodology.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400810
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    Analysis of coupled cluster and quadratic configuration interaction theory in terms of sixth-order perturbation theory (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 43-70 
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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: The energy at sixth-order Møller-Plesset (MP6) perturbation theory is given and dissected into 36 size-consistent energy contributions resulting from single (S), double (D), triple (T), quadruple (Q), pentuple (P), and hextuple (H) excitations. It is shown that MP6 is an O(N9) method, but less costly approximations to MP6 are possible. MP6 is used to analyze and compare coupled cluster (CC) and quadratic configuration interaction (QCI) methods, namely CCD, CCSD, CCSD(T), CCSD(TQ), CCSDT, CCSDT(Q), CCSDT(QQ), QCISD, QCISD(T), and QCISD(TQ). For larger molecules and molecules with distinct T contributions, CCSD is significantly better than QCISD because CCSD covers a relatively large number of T contributions and in particular T,T coupling effects at sixth order. Differences between the two methods become larger at higher orders of perturbation theory. If T and Q excitations are included in QCISD and CCSD in a noniterative way - thus leading to QCISD(T), CCSD(T), QCISD(TQ), and CCSD(TQ) - then differences between QCI and CC decrease. Hence, if a given molecular problem depends on the inclusion of T effects, improved calculational results will be obtained in the following order: MP4(SDTQ) 〈 QCISD(T) 〈 CCSD(T) 〈 QCISD(TQ), CCSD(TQ) 〈 CCSDT. None of the methods investigated is correct in sixth order. Only if CCSDT is extended to CCSDT(QPH), which is also an O(N9) method, are all MP6 energy contributions then covered.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400809
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    Bounds to the energy of quantum-mechanical models from variational functionals (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 95-106 
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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 derive semiclassical energy functions in configuration space that provide upper or lower bounds to the energies of quantum-mechanical systems. The bounds are predicted by rigorous theorems about the local energy which we choose to depend on adjustable parameters in order to improve the accuracy of the results. We apply the method to one-dimensional models, central-field systems, and the Zeeman effect in hydrogen.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400812
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    Solution of the time-dependent Schrödinger equation using a continuous Fourier transform (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 107-111 
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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 the solution of the time-dependent Schrödinger equation. The split operator method is used to propagate an initial wave function and the continuous Fourier transform is applied to obtain the energy eigenvalues. High resolution in the energy is obtained without line shaping techniques.s
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400813
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    Kinetic balance in contracted basis sets for relativistic calculations (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 131-139 
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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 demonstration of kinetic balance failure in heavily contracted basis sets is given. Other possible methods of constructing small component basis sets for 4-component relativistic calculations are discussed. The position of the additional negative energy levels in extended balance calculations in some recent many-electron calculations is examined.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400816
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    Relativistically parameterized extended Hückel calculations. 13. Energy bands for uranium compounds UB2, UB4, UC, UBC, and UPt3 (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 121-130 
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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 extension of the relativistically parameterized extended Hückel method REX to systems with translational symmetry is reviewed. This extension (REXBAND) is then applied to the description of the electronic structures of a number of heavy-element solids, namely UB2, UB4, UC, UBC, and UPt3.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400815
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    Sensitivity of time-dependent vibrational dynamics to curve-crossing topology (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 141-153 
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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 quantum time evolution in a two-state curve-crossing situation can be computed with the split operator FFT method. We present a version of that scheme that is based on the analytic exponentiation of two-by-two matrices. We use this approach to investigate the vibrational dynamics of the coupled b′, c′1 Σu+ states of the N2 molecule. We focus our study on the sensitivity of time-dependent transition amplitudes to the features of the curve-crossing topology.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400817
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    Effects of basis set contraction on relativistic and Breit interaction energies (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 113-120 
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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: Relativistic self-consistent field (SCF) calculations have been performed on a number of neutral and ionized atoms with basis sets of contracted and uncontracted Gaussian-type functions. Both Dirac-Fock and Dirac-Fock-Breit SCF calculations have been performed with the intent of observing to what extent basis set contraction affects the calculated relativistic and Breit interaction contributions to total atomic energy. It is found that extensive basis set contraction has relatively little effect on the calculated relativistic and Breit interaction energies.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400814
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    Ladder operators for central potential wave functions from the algebraic representation of orthogonal polynomials (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 155-164 
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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 general algebraic procedure that yields to raising and lowering operators for the solutions of second-order differential equations is presented. The method is illustrated by applying it to the differential equations of Hermite and Laguerre polynomials. Taking advantage of the algebraic representation of these polynomials, the ladder operators for harmonic oscillator and hydrogen atom wavefunctions are straightforwardly deduced without resorting to specialized factorizations. The proposed algebraic approach can be extended to the determination of new sets of ladder operators that could be used in the calculation of matrix elements in specific applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400818
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    Electron transfer in macromolecules: Green's function and diagrammatic techniques (continued fraction representation) (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 183-192 
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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 applied special graphical technique to investigate the influence of side/end groups of macromolecules upon long range electron transfer. We show that in case of acyclic side/end groups the Green function may be cast in the form of continued fraction, similarly to the result of electron transfer in random media. The structure of continued fraction correlates exactly to the side/end graph's structure. The rules of graphical construction of Green functions (which are solutions of Schwinger-Dyson equations) are presented in concise form.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400820
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    An examination of the effects of basis set and charge transfer in hydrogen-bonded dimers with a constrained Hartree-Fock method (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 193-207 
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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: Constrained Hartree-Fock methods in which orbitals are constructed from strictly local nonorthogonal subsets of the molecule's atomic orbital basis have been known for over a decade. These methods have been principally used to generate localized molecular orbitals and interpret intramolecular interactions. In this paper, constrained Hartree-Fock results from basis sets ranging from minimal to extensive are presented for hydrogen-bonded dimers in which individual molecular orbitals are constructed from atomic orbitals belonging to individual monomers. These calculations eliminate both basis set superposition errors (BSSE) as well as charge transfer between monomers. This allows one to examine the effects of basis sets on the electrostatic and polarization components to the energy unmasked from BSSE. The charge transfer components are also isolated by comparing results to unconstrained calculations near the Hartree-Fock limit, where BSSE is vanishingly small. Finally, at moderate intermolecular separations when charge transfer becomes negligible, the constrained results are compared to both counterpoise-corrected and unconstrained calculations.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400821
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    Perturbation theory of intermolecular interactions: Are second-order Rayleigh-Schrödinger energies meaningful? (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 165-181 
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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 interactions between atoms are so strong that they create an infinite number of unphysical states of lower energy than the physical ground state, thus raising the question of the significance of second and higher order perturbation energies. We have carried out a series of configuration interaction calculations which shed light on this question and other questions regarding the perturbation theory of intermolecular interactions. The calculations used an unconventional set of configuration functions, each being the product of two Slater determinants, one for each atom. This makes it possible to calculate approximations to both unphysical and physical states, and to follow the changes in eigenstate energies as the interaction is turned on between atoms. We report results for LiH which show that eigenvalues of Ĥ0 + λV̂, where Ĥ0 is the sum of atomic Hamiltonians and V̂ the interaction potential, undergo avoided crossings between λ = 0 and 1. The perturbation expansion of the ground state energy must become divergent at the first avoided crossing, λ = 0.76. In addition, we report results of calculations with three effective Hamiltonians which have all unphysical state energies shifted into the physical continuum. They show no avoided crossings between the ground state and other states until λ is almost equal to 1. The perturbation expansion derived from one of these effective Hamiltonians is shown to have several desirable properties which the expansions derived from the other two lack. Its one fault is that it must diverge at λ = 1, where an avoided crossing occurs. This avoided crossing is related to the exchange symmetry of electrons. The implications of our results for the meaning of second-order perturbation energies and for the development of convergent exchange perturbation methods is discussed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400819
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  • 98
    Electronic Resource
    Electronic Resource
    Symbolic computation in physics and chemistry: Applications of the inner projection technique and of a new summation method for divergent series (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 209-223 
    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 goal of this article is to illustrate the use of symbolic computation in solving problems in physics and chemistry. For instance, the application of the inner projection technique combined with renormalization is shown to give very tight bounds for the ground-state energy of anharmonic oscillators. Some typical results are presented. Further, it has been observed that inner projection is directly applicable to the PPP and Hubbard Hamiltonians. The results for the model of benzene are briefly presented. A new method for summing divergent series, which we call the Weniger summation method, is proposed. This method is used, with excellent results, for the summation of divergent perturbation series for the energy of anharmonic oscillators. This method is also applied for the summation of the divergent series corresponding to the ground-state energy of the Hubbard Hamiltonian of the infinite chain. Other applications of the Weniger summation method to diffusion and heat conduction problems are summarized.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400822
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  • 99
    Electronic Resource
    Electronic Resource
    Calculation of molecular geometries and energies by a local density functional approach (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 249-259 
    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 used density functional theory in the local density approximation, as implemented in the DMol-double numerical plus polarization (DMol/DNP) procedure, to calculate optimized geometries for a group of molecules containing only first-row atoms. The results are in generally satisfactory agreement with experimentally determined structures. The DMol/DNP atomic and molecular energies are rather poor, when compared to high-level ab initio GAUSSIAN 1 values (which are taken as the standard), but the errors do show excellent linear correlations with the total energies. These relationships allow the DMol/DNP results to be corrected to a high degree of accuracy, so that they can then be used to obtain atomization and dissociation energies that compare well with measured values. It is shown that the errors in the DMol/DNP energies tend to increase as the number of electrons becomes larger and the number of nuclei smaller.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400825
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  • 100
    Electronic Resource
    Electronic Resource
    Algebrants in many electron quantum mechanics. II. New computational algorithms (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 225-234 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Algebrants are generalized matrix functions; they are multilinear forms of which the determinant, the permanent, and the immanant are special cases. A formal definition and fundamental properties of algebrants was given in paper I of this series. The present work develops algorithms for computation of those algebrants that arise in computational spin-free quantum chemistry for valence bond (VB) wave functions built on nonorthogonal orbitals. Namely, we exploit the left- and right-hand antisymmetry of N P N ˚A to develop algorithms that greatly reduce or eliminate the N! problem. The algorithms can be implemented in any computer language; our implementation in FORTRAN is available upon request. The savings effected by spin-free vs Slater determinant versions of VB theory are illustrated for 2, 3, …, 10 electrons.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400823
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