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  • 1
    Digitale Medien
    Digitale Medien
    On the performance of high-level correlated single-reference methods: The energy, dipole moment, and polarizability functions of BH (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 7300-7305 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The performance of the fourth-order many-body perturbation theory (MBPT) and different coupled cluster (CC) methods in calculations of the potential energy and electric property functions has been investigated for the X 1Σ+ state of the BH molecule. In spite of the single reference approximation most of these methods are capable of correctly predicting the shape of the energy and property functions. Both the qualitative features of these functions and their numerical values are considerably improved on passing from the MBPT to the CC models. The stability with respect to the near degeneracy of the reference state has been found to increase in the same way. Excellent results are obtained from the CC calculations for the potential energy and electric properties of the BH molecule in the vicinity of the equilibrium bond distance.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.456208
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  • 2
    Digitale Medien
    Digitale Medien
    Optimized virtual orbital space for high-level correlated calculations. II. Electric properties (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5749-5758 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The optimized virtual orbital space (OVOS) technique recently proposed for high-level correlated calculations of energy surfaces, is shown to be nearly as efficient for electric field properties. In particular, the polarizability of F−, and the dipole moment and polarizability of FH as a function of internuclear separation are studied. A reduction of the virtual space to about one-half has a negligible effect on the dipole moment and polarizabilities for FH and F− examples. A further reduction to one-quarter is reliable when augmented with the exact second-order result, obtained as a by-product of the OVOS generation. This enables the extension of high-level correlated methods to systems at least 2–4 times larger than those that could be accurately studied using the full space of virtual orbitals.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.454721
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  • 3
    Digitale Medien
    Digitale Medien
    A theoretical study of the A 1Π←X 1Σ+ system of SiH+ (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 423-432 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Theoretical studies have been performed on the X 1Σ+ and A 1Π states of SiH+. The complete active space, self-consistent field (CASSCF) and many-body perturbation theory (MBPT) methods were employed for the X 1Σ+ and state while the A 1Π excited state potential energy curve was studied by using CASSCF, multireference contracted configuration interaction (MR CCI, (MR CEPA), and coupled pair functional (CPF) approaches. Excellent agreement was obtained with experiment for the X state spectroscopic parameters (CASSCF): re=1.505 (1.50 A(ring); D0=3.30 (3.22±0.03) eV; ωe=2161 (2155) cm−1; ΔG1/2=2093 (2089) cm−1, with experimental values within parentheses. The shape of the potential curve for the A state was very sensitive to the basis set and higher order electron correlation. The best results, obtained with the CPF method, were re=1.888 (1.871) A(ring); D0=0.15 (0.15±0.03) eV; ωe=438 (448) cm−1; ΔG1/2=318 (389) cm−1. The computed f0,0 oscillator strength for the A←X transition was 1.2×10−3 which falls between the laboratory value, (2.4±1)×10−3, and a value obtained from the solar spectrum, 0.5×10−3. The computed life time for the v'=0 state is 956 ns to be compared to the experimental value 1025±80 ns.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.455483
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  • 4
    Digitale Medien
    Digitale Medien
    Polarized basis sets and the calculation of infrared intensities from nuclear electric shielding tensors (1985)
    Springer
    Theoretical chemistry accounts 68 (1985), S. 431-444 
    Details
    ISSN: 1432-2234
    Schlagwort(e): Basis sets ; Perturbation-dependent basis sets ; Polarized basis sets ; Hellmann-Feynman theorem ; Infrared intensities ; Molecular properties ; H2O
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The idea of the basis set polarization which follows from the known dependence of basis set functions on the perturbation strength is applied to the calculation of the dipole moment derivatives with respect to nuclear displacements. The differentiation of the dipole moment function is replaced by the straightforward evaluation of derivatives of the intramolecular electric field with respect to the external electric field strength. The method and its efficiency are illustrated by a series of calculations of the dipole moment derivatives for the water molecule. Already a polarized basis set of 26 CGTO's derived from the minimal CGTO basis set provides fairly reasonable results.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00527668
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  • 5
    Digitale Medien
    Digitale Medien
    Electric properties of the chloride ion (1988)
    Springer
    Theoretical chemistry accounts 74 (1988), S. 185-194 
    Details
    ISSN: 1432-2234
    Schlagwort(e): Multipole polarizabilities ; Properties of Cl− ; Polarized basis sets ; MBPT calculations of properties
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The dipole (α), quadrupole (C), and dipole-quadrupole (B) polarizabilities and the dipole hyperpolarizability (γ) of the chloride ion have been calculated by using the many-body perturbation theory approach and a series of large polarized GTO/CGTO basis sets. The complete fourth-order treatment of the electron correlation effects with a basis set comprising the s, p, d, f, and g functions gives: α=38.01 a.u., C=211.5 a.u., B=−5.14×103 a.u., and γ=128. 5×103 a.u. as compared to the corresponding SCF values (α=31.49 a.u., C=158.9 a.u., B=−2.92×103 a.u., γ=57.7×103 a.u.). The quenching of polarizabilities of the Cl− ion in solutions and ionic crystals is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00527142
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  • 6
    Digitale Medien
    Digitale Medien
    Time-dependence of wave functions and the calculation of transition intensities (1989)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 35 (1989), S. 409-423 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The standard formalism of the perturbation theory for time-dependent perturbations follows from the assumption that the exact solution of the unperturbed time-independent problem is known. The consequences of this assumption are analyzed.Particular attention is given to the methods used for the evaluation of transition intensities. It is shown that the traditional intensity formula in most cases violates the assumptions underlying its derivation. It is shown that for the given ansatz concerning the form of the approximate wave function, the transition intensities should be determined from the variation treatment of the corresponding time-dependent problem. The wave functions of both states involved in the transition should be given the same amount of variation flexibility. This condition is satisfied if the transition intensity expression follows from the complete timedependent perturbation treatment of the perturbed system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/qua.560350306
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