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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 32 (1987), S. 669-676 
    ISSN: 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: While calculating zero-field splitting terms for the lowest triplet state of 4H-pyran4-thione, at the experimental geometry, it was found that the ground state was unstable with respect to an unrestricted Hartree-Fock perturbation. The smallest fragment of the molecule retaining this instability was found to be diatomic CS. The instability is dependent on the basis set used for the calculation. The instability and its relationship to basis set, equilibrium geometry, and the importance of polarization functions for second row elements has been explored for CS and H2CS as a function of internuclear distance. Minimal basis set calculations involving second row elements may be particularly prone to such instabilities.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 7 (1973), S. 1045-1050 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The general problem of the transfer of the representation of a set of orthonormal functions from one basis to a different, nonequivalent one is considered and specialized to a matrix formulation convenient for use in molecular electronic structure calculations. A procedure is suggested for treating problems where the transfer of representation breaks into a subset of most interest and one of less interest as for example the occupied and virtual orbitals of a Hartree-Fock SCF calculation. These techniques are then applied to obtain a representation of a methyl group from an SCF wave function for methane.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 19 (1981), S. 179-189 
    ISSN: 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: Energy difference formulas for isoelectronic processes are derived using a perturbation series. The perturbed Hamiltonian is written as a function of a perturbation parameter that changes linearly from zero to one between the limits of the isoelectronic process. The perturbation series is based on a zero order wave function obtained when the perturbation parameter has a value of ½. For the description of changes of electronic energy with internuclear geometry, this zero order wave function will correspond to the solution of a Hamiltonian which contains atoms from both internuclear geometries, but with half their normal nuclear charge. Energy differences calculated with this formalism for the stretching of simple diatomic molecules hydrogen fluoride, fluorine, and carbon monoxide and the rotational barrier in ethane are compared with results from restricted Hartree-Fock and integral-Hellmann-Feynman theorem energies.
    Additional Material: 1 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 613-625 
    ISSN: 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 review the progress which was made during the last 6 years in the attempts to use electron diffraction data to gain insights into the electronic charge densities of isolated molecules and their moments. In regard to theory, we investigated the sensitivity of the elastic differential high-energy cross sections to the basis sets in the wave function calculations. Extensive calculations on H2O showed that there is no significant change by the molecular vibrations on the static charge density deformation maps. Finally new relations could be derived which allow the determination of nuclear and electronic moments from the differential cross sections at small angles. In regard to experimental data, new sets of purely elastic cross sections are available for He, Ne, CO2, N2, and CH4, which are compared with Hartree-Fock and limited configuration interaction wave function results. The differences are discussed. New experimental values for some moments for N2 and CH4 are reported.
    Additional Material: 13 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 287-298 
    ISSN: 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.
    Type of Medium: Electronic Resource
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