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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 198-210 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dipole moment, parallel dipole polarizability, and the parallel first hyperpolarizability of the coinage metal hydrides (CuH, AgH, AuH) are studied in the context of their vibrational contributions. The partition of the property values into pure electronic, vibrational averaging, and pure vibrational terms is discussed, and the corresponding contributions are calculated by means of the field-dependent Numerov–Cooley integration technique. The potential energy and property surfaces, required for the evaluation of these contributions, follow from different high-level electronic structure calculations. Parallel to the nonrelativistic studies, a relativistic treatment of the investigated properties has been carried out. It has been found that relativistic effects significantly reduce the magnitude of the vibrational corrections to the studied properties. A particularly large relativistic reduction has been found for the vibrational contribution to the first hyperpolarizability. The relativistic effect is enhanced with increasing nuclear charge of the heavy atom, and can be interpreted in terms of the relativistic effect on the potential energy and electric property curves. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 1645-1654 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We demonstrate how vibrational contributions to any (static) electric property may be computed with respect to an arbitrary reference geometry which, at a given level of electronic structure theory, need not correspond to the associated minimum energy geometry. Within the harmonic approximation, it is shown that the formulas for the vibrational contributions can be extended to include a second-order corrective term, which is a function of the energy gradient and the (nuclear) first derivatives of the property in question. Taking the BH molecule as a test case, we illustrate that the order of magnitude of the correction increases with order of property (i.e., μ(approximate)10−2→γ(approximate)101−102), and that this value is equivalent to the difference in (pure) electronic contributions evaluated with respect to the optimum and nonoptimum geometries. Furthermore, we show that for a diatomic, vibrational [zero-point vibrational average (ZPVA) and pure] contributions computed at a nonoptimum geometry may be readily corrected to give the optimum geometry values. Thus we provide a route for obtaining total (electronic+vibrational) properties associated with a minimum energy geometry, using information calculated at a nonoptimum geometry. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 1845-1859 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electronic, vibrational and rotational contributions to the dipole moment μ, polarizability α, and first and second hyperpolarizabilities, β and γ, are presented for the boron hydride molecule; static and dynamic rovibrational properties are reported for the first time. The electronic contributions are computed ab initio by finite differencing the electronic energy computed at the Hartree–Fock level of theory, and using various sophisticated correlated methods. Specifically these are Møller–Plesset perturbation theory at second order, and fourth order (including single, double, triple and quadruple substitutions), and the Brueckner variant of the coupled-cluster method including triple excitations; density functional theory with the B3LYP functional is used for comparison. Vibrational (and rotational) contributions to the properties are calculated at the Hartree–Fock level of theory; for the vibrational properties, electron correlation is partially included using second order Møller–Plesset theory. Basis set and electron correlation effects on both electronic and vibrational contributions are assessed and discussed. The dependence of the vibrational properties on the mechanical and electrical anharmonicity is examined, and the two methods used in its computation — a finite difference approach and a perturbation theoretic method — are compared and contrasted. A brief analysis of the frequency dependence of vibrational contributions to α(−ωσ;ω1), β(−ωσ;ω1,ω2) in the electro-optic Pockels and second harmonic generation effects, and γ(−ωσ;ω1,ω2,ω3) in the electro-optic Kerr and electric-field-induced second harmonic generation effects, is presented. The electronic results are compared with literature values believed to the best currently available; agreement is shown to be acceptable. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 9200-9213 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We describe our implementation of the Zhao, Morrison, and Parr method [Phys. Rev. A 50, 2138 (1994)] for the calculation of molecular exchange-correlation potentials from high-level ab initio densities. The use of conventional Gaussian basis sets demands careful consideration of the value of the Lagrange multiplier associated with the constraint that reproduces the input density. Although formally infinite, we demonstrate that a finite value should be used in finite basis set calculations. The potential has been determined for Ne, HF, N2, H2O, and N2(1.5re), and compared with popular analytic potentials. We have then examined how well the Zhao, Morrison, Parr potential can be represented using a computational neural network. Assuming vxc=vxc(ρ), we incorporate the neural network into a regular Kohn–Sham procedure [Phys. Rev. A 140, 1133 (1965)] with encouraging results. The extension of this method to include density derivatives is briefly outlined. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 57 (1996), S. 533-542 
    ISSN: 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 performance of numerical basis sets in relation to Gaussian basis sets is examined, by studying 20 small sulfur-containing molecules. The results of geometry optimization calculations are reported for each molecule using both density functional and Hartee-Fock methods. In comparison with experimental data, it is shown that the use of numerical bases tend to overestimate structural parameters, particularly bond lengths, and, in most cases, more than Gaussian basis sets. It is also shown that the use of a larger Gaussian basis set in DFT calculations has the effect of reducing bond lengths. © 1996 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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