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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 1247-1252 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theoretical background to the scaling procedure used for correcting molecular force constants computed at the Hartree–Fock (HF) level is presented, in which scaling is considered as an empirical simulation of the effect of electron correlation. Using a variational formalism for the analytical first and second derivatives, it is shown that a successful scaling requires (i) relatively large exact excitation energies; (ii) a singlet-stable solution for the HF ground state; and (iii) molecular orbitals that can be well localized for the ground electronic state. The relationship between the exact nonrelativistic and HF limit values of the quadratic force constants has been investigated when the above conditions are satisfied. A single multiplicative (scale) factor is required at this limit and its value is approximately C20 near the "exact'' equilibrium geometry, where C0 is the coefficient of the HF determinant in a complete configuration interaction expansion. This approach requires a moderate size of the molecules investigated. A specific numerical example is considered.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 17544-17550 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 843-852 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Some features of the multipole expansion of the Coulomb potential V for a system of point charges are studied. It is shown that multipole expansion is convergent both locally in L2(R3) and weakly on some classes of functions. One-particle Hamiltonians Hn = H0 + Vn, where H0 is the kinetic energy operator and Vn is the n-th partial sum of the multipole expansion of V, are discussed, and the convergence of their eigenvalues to those of H = H0 + V with increasing n is proved. It is also shown that the discrete spectrum eigenfunctions of Hn converge to those of H both in L2(R3) (together with their first and second derivatives) and uniformly on R3. © 1996 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 11 (1977), S. 1-15 
    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 influence of errors in molecular integrals on the calculated RHF energy values is considered for two models which correspond to round-off and shift errors. The energy variations induced by errors in elements of one- and two-electron matrices and the overlap matrix are represented in a quadratic approximation and the same degree of accuracy is maintained for mean values and standard deviations. The formulas given point out that mean values are less than zero when some of the errors are non-shifted. Special care is required when Gaussian lobe functions are used.
    Type of Medium: Electronic Resource
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