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  • Atomic, Molecular and Optical Physics  (7)
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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979), S. 65-70 
    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: Pair energies contributing to the correlation energies of the outer-shell electrons (n = 3) as well as for the 1s2 and 2s2 pairs are computed for the Zn2+ closed-shell ion by means of the variational-perturbation method starting with the sum of one-electron Hartree-Fock operators as the zeroth-order Hamiltonian. The results allow an understanding of the electron correlation for pairs of electrons of the p and d type. For 3p3d pairs it has been found that the correlation energy for the singlet pair of 1D symmetry is lower than for the triplet pair 3D. The 3l-3l′ correlation energies are compared with the MBPT results of Kelly and Ron for Fe. The total correlation energy of the outer shell is -1.032 a. u.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 21 (1982), S. 753-765 
    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 derive basic integrals needed for calculation of matrix elements of the Fourier transformed Coulomb operator and the Fourier transformed square of the Coulomb operator between 1s Slater functions. These integrals arise, for example, in the momentum space (k space) susceptibility formulation of van der Waals forces. The advantages of integration in k space (rather than r space) are that in k space there is a drastic reduction in the number of integration variables, and contour integration can be used. The derivation is completely analytic and the auxiliary integrals are all obtained in closed form.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 279-288 
    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 pair correlation energies for some nl4f pairs of the ground state of the Yb atom are calculated for the first time. The partial wave (PW) increments to the second-order pair energies are generated using numerical first-order radial pair functions obtained as the solution of two-dimensional differential equations. The analysis of the PWs contributions shows the dominant role of the df, fg, and gh PWs for the 4d4f pair, of the pf and dg PWs for the 4p4f and 5p4f pairs, and of the sf and pg PWs for the 4s4f, 5s4f, and 6s4f pairs. A discussion of the similarities and differences of the structure of the correlation energy found in this paper with those calculated earlier for smaller atoms is given.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 27 (1985), S. 665-675 
    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: Second-order Rayleigh-Schrödinger Hartree-Fock perturbation theory is applied to evaluate the correlation energy for the 4f14 shell of Yb. The partial-wave (PW) increments to the pair energies, and the total correlation energy are calculated using first-order radial pair functions obtained as the solution of two-dimensional differential equations. These equations are solved using the Chalmers University version of the finite difference method. The total second-order correlation energy amounts to 0.89573 hartree. The results for the pair energies, which are close to the all-external pair energies, are compared with related CI values. It turns out that the correlation effects within the 4f shell of rare-earth systems are dominated by the all-external effects. The ff and gg PWS are dominant in the description of the correlation effects in the 4f shell and provide 80% of the total correlation energy. Next in importance are the dd, hh, and dg PWS which provide 12% of the total correlation energy.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 59 (1996), S. 239-249 
    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 impact of the choices of the complete model space (CMS) and of the orbital basis set on the existence, attainability, and properties of the nonstandard solutions of the valence-universal coupled-cluster (VU-CC) methods has been studied for the case of nonlinear equations corresponding to the atomically oriented form of these methods accounting for one- and two-electron excitations (VU-CCSD/R method) and applied to the Be atom. The results for five 1S states are discussed. In addition to the previously applied CMS defined by the orbital set (2s, 2p) and (2s, 3s), we have employed the CMSs defined by the (2s, 2p, 3s) set. For each of the CMSs several nonstandard solutions are documented. It is found that the energies of the individual states corresponding to standard and nonstandard solutions differ very little. These energies are also almost independent on the choice of CMS. On the other hand, the energies of excited states disclose a strong dependence on the radial structure of the orbital basis set. It is also demonstrated that the magnitudes of the cluster amplitudes representing a set of states depend both on the choice of the CMS and whether they correspond to the standard or nonstandard solutions. © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 59-72 
    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: Sets of nonlinear equations for the cluster amplitudes of the valence-universal coupled-cluster (VU-CC) method have been solved to obtain physically meaningful multiple solutions for Be, B+, and C2+. The wave operator is taken in Lindgren's normal ordered exponential form and the completeness of the model space is postulated. The cluster operator is restricted to its one- and two-electron components that are represented in terms of radial amplitudes defined by the configurational excitations (VU-CCSD/R method). Five solutions giving rise to 10 approximate energies of four 1S states are obtained and discussed. These are the first multiple solutions documented for a nonmodel system. Some attention is paid to the problem of the efficiency of various methods in obtaining alternative solutions and to some consequences of the availability of alternative solutions. © 1993 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 55 (1995), S. 269-275 
    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 recently formulated atomically oriented valence-universal theory (VU-CCSD/R) based on various complete model spaces is applied to the accurate description of the 2s2 1S, 2s3s 1S, 2p2 1S, and 3s2 1S states of Be. Two extensive 9s9p7d7f5g STO basis sets that differ by one s-type function are employed. Both standard and nonstandard solutions of the VU-CC equations are considered. The eight values of the ground-state energies obtained when considering various model spaces and basis sets were found to differ very little. The energies of the individual excited states disclosed a relatively weak dependence on the choice of model spaces defining the method (or, equivalently, on the fact whether they correspond to standard or nonstandard solutions). In turn, the energies of the excited states strongly depend on the STO basis set used in the calculations. To obtain a reliable description of both the ground state and excited states, well-balanced STO basis sets have to be employed. © 1995 John Wiley & Sons, Inc.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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