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  • 1
    Electronic Resource
    Electronic Resource
    Infinite-order two-component theory for relativistic quantum chemistry (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 2696-2704 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method for the iterative algebraic generation of the numerically accurate two-component Hamiltonian for the use in relativistic quantum chemistry is presented. The separation of the electronic and positronic states of the Dirac Hamiltonian is accomplished by the algebraic solution for the Foldy–Wouthuysen transformation. This leads to the two-component formalism whose accuracy is primarily limited by the choice of basis functions. Its performance is tested in calculations of the most sensitive 1s1/2 energy for increasing values of the nuclear charge. These calculations show that the electronic part of the Dirac eigenspectrum can be obtained from the two-component theory to arbitrarily high accuracy. Moreover, if needed, the positronic states can be separately determined in a similar way. Thus the present method can be also used for the evaluation of quantum electrodynamic corrections in the finite basis set approximation. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1436462
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  • 2
    Electronic Resource
    Electronic Resource
    Static dipole polarizability of the fluoride ion (1979)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 83 (1979), S. 1653-1657 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100475a015
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  • 3
    Electronic Resource
    Electronic Resource
    Molecular electric polarizabilities (1978)
    Springer
    Theoretical chemistry accounts 47 (1978), S. 205-216 
    Details
    ISSN: 1432-2234
    Keywords: Electric field variant Gaussian orbitals ; Molecular polarizabilities ; Molecular dipole moments ; SCF perturbation theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The electric field variant (EFV) Gaussian basis sets of double-zeta (2-ζ) quality are used for the calculation of the electric dipole polarizabilities of diatomic molecules in the Hartree-Fock approximation. The explicit external electric field dependence of the GTO basis set, introduced according to the method described in Part I of this series, is shown to account for the major portion of the electric field induced deformation of the wavefunction. The Polarizabilities obtained in the present calculations are quite close to the best Hartree-Fock results. The deviations from near-Hartree-Fock values amount to 3–8 per cent for the parallel component and to 10–15 per cent for the perpendicular one. It was also shown that the same method leads simultaneously to a considerable improvement of the dipole moments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00577162
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  • 4
    Electronic Resource
    Electronic Resource
    Coupled multiconfiguration self-consistent field (MC SCF) perturbation theory (1975)
    Springer
    Theoretical chemistry accounts 40 (1975), S. 157-174 
    Details
    ISSN: 1432-2234
    Keywords: MC SCF perturbation theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The analytical form of the perturbation theory for the MC SCF method of Veillard and Clementi is presented. The appropriate second-order energy functional which takes into account the self-consistency requirements, leads to a set of coupled first-order perturbed equations determining the perturbed configuration coefficients and orbitals. The second-order energy formula derived from this functional can be given a clear physical interpretation. The present analytical approach is compared with the finite perturbation MC SCF scheme. The possibility of the approximate solution of the coupled MC SCF perturbation equations is also discussed and the so-called uncoupled procedures are devised. In the limit of the single determinant wave function the present formulae are shown to be equivalent to the appropriate Hartree-Fock perturbation results. The differences between the one-configuration SCF and the MC SCF approach are illustrated by the calculation of the electric dipole polarizability of. HZ in the CNDO/2 approximation. It is shown that the one-configuration SCF approaches cannot account for the correct asymptotic properties of the second-order energy for large internuclear distances. This feature of the SCF perturbation theories does not depend on the specific approximations of the CNDO/2 scheme and is corrected by using the MC SCF perturbation theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01135886
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  • 5
    Electronic Resource
    Electronic Resource
    Analytic techniques for the coupled multiconfiguration SCF perturbation theory (1977)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 11 (1977), S. 233-245 
    Details
    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 perturbation theory based on the paired excitation multiconfiguration self-consistent field approach of Clementi and Veillard is considered. The coupled first-order perturbed orbital equations are analysed and an appropriate computational scheme for their solution is discussed. The proposed computational scheme is analogous to the technique employed for the solution of the coupled Hartree-Fock equations in the one-configuration approximation. However, because of the presence ofnondiagonal Lagrangian multipliers and the use of different one-electron operators for different orbitals, the present scheme raises some new computational problems. In this context a new technique for the solution of the unperturbed multiconfiguration self-consistent field equations is proposed. A simple illustration of the superiority of the multiconfiguration perturbation approach with respect to the ordinary coupled Hartree-Fock scheme is given. Also the validity of the variation formulation of the presented scheme and its relation to the finite-field approach are discussed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560110204
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  • 6
    Electronic Resource
    Electronic Resource
    Variable basis sets in perturbation theory: Numerical finite perturbation versus analytic approach (1979)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 15 (1979), S. 147-167 
    Details
    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 consider the problem of determining variational, external-field-dependent corrections to nonoptimal zero-field nonlinear parameters. Both a direct analytic perturbation analysis and finite perturbation methods are described in a general way and in detail for the SCF approximation. The abstract theory is illustrated by reference to the results of several explicit calculations. Also, the sensitivity of the results to the choice of zero-field values is discussed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560150203
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    Paper (German National Licenses)
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