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  • 1
    Electronic Resource
    Electronic Resource
    Integration points for the reduction of boundary conditions (1973)
    Springer
    Theoretical chemistry accounts 31 (1973), S. 195-200 
    Details
    ISSN: 1432-2234
    Keywords: Numerical integration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An analysis of a method for the numerical evaluation of the integral $$\int\limits_a^b { f\left( x \right)} dx$$ is presented. The method introduces a change of variable, x = x(q), with the property that d nx/dqnis zero at x = a, x = b for n = 0, 1, 2,... N, where N is an integer to be chosen. The Euler-Maclaurin formula shows that the resulting integral in the variable q is ideally suited for numerical integration, using equally spaced points and equal weights in q-space. Examples are given for various integrals which occur in quantum chemistry and applications to more than one dimension are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00526508
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    A method for selection and use of numerical integration points for molecules with cylindrical symmetry (1973)
    Springer
    Theoretical chemistry accounts 31 (1973), S. 201-204 
    Details
    ISSN: 1432-2234
    Keywords: Transcorrelated method ; Numerical integration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Boys and Handy [1] have discussed the solution of the bivariational equations with restricted numerical integration. One of the weaknesses of the method was that in the numerical summations over points, some points arose with r ij= 0 and non-zero weights. This makes the method quite impractical for the Schrodinger Hamiltonian (because of the singularity at r ij= 0), and it cannot be advantageous for the transcorrelated Hamiltonian C−1HC because there will be some discontinuous higher derivatives at r ij=0. Here it is shown how the symmetry of cylindrically symmetric molecules can be used to eliminate such points, without losing any of the advantages of the overall method, such as the convergence of the eigensolutions. It is also shown how the primary numerical integration points (z i, ri) may be chosen in any calculation such that each is associated with an equal amount of one-electron density. The choice of the angular coordinates are governed by the removal of the r ij=0 points and maintaining the natural orthogonality between orbitals of different symmetry types. The method has been programmed and found to be practical, although no new molecular calculations have yet been performed. It is to be hoped that these points will give a basis for new transcorrelated calculations on diatomic molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00526509
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Hydrogen-bonded complexes involving HF and HCl: the effects of electron correlation and anharmonicity (1987)
    Springer
    Theoretical chemistry accounts 71 (1987), S. 41-57 
    Details
    ISSN: 1432-2234
    Keywords: Hydrogen bonds ; Frequency shifts ; Anharmonicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Calculations on the hydrogen-bonded complexes HCN⋯HF, H2O⋯HF, ClCN⋯HCl and (CH3)2O⋯HCl are reported. SCF harmonic values for the HF and HCl frequency shifts are in considerable disagreement with experiment, by as much as 100 cm−1. Calculations at the MP2 (harmonic) level yield improved agreement with experiment, reducing discrepancies to the order of 10 cm−1. We have also calculated all the cubic and quartic force constants for HCN⋯HF at the SCF level, so that the anharmonic constants, x rs can be evaluated. Although x 11 (v 1=H-F stretch) is large and negative, it is more than compensated by a positive x 16 (v 6=N⋯H-F bend), so that the anharmonic correction to v 1 is small and positive. The validity of these anharmonistudies is examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00538480
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    Paper (German National Licenses)
    Fulltext
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