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  • Computational Chemistry and Molecular Modeling  (4)
  • 31.50. + w  (1)
  • 33.10. - n  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 36 (1989), S. 255-263 
    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 isotropic (aiso) and dipolar (Adip) hyperfine coupling constants of 19F2- were obtained from MRD-CI wave functions using a variety of basis sets. In series I, increasing numbers of d functions were added to a 5s4p contracted Huzinaga/Dunning basis. In series II, the 5s3p basis set was uncontracted in several steps until 9s5p was reached, to which were added from one to three d-polarization functions. CI parameters (selection thresholds and the number of reference configurations) were also varied. A study of the R dependence of aiso and Adip was performed. The best values obtained at Re are 260 G for aiso and 308 G for Adip, compared with experimental values of about 280 G for aiso and 320 G for Adip.
    Additional Material: 8 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 11 (1977), S. 743-752 
    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: A series of five different Iterative Natural Orbital (INO) procedures are tested for the ground state of water and are compared on the basis of their respective convergence properties. The choice of configuration space employed in these methods is shown to be a key factor in determining the results of such calculations. If the CI space is generated by taking all single excitations with respect to a series of dominant or reference configurations, it is concluded that the practice of varying such generating species at each iteration is highly desirable. In general the choice of the configuration space is found to be much more important than the attainment of strict NO convergence, whereby experience indicates that inclusion of all singly and doubly excited configurations (or at least a select subset thereof) relative to a series of dominant configurations provides the most efficient means of approximating the true NOS of a given system within the general INO framework.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 41 (1992), S. 413-419 
    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: Ab initio MRD-CI calculations using a basis set of near Hartree-Fock quality have been carried out to calculate the ground-state electronic structure of S2N+, S2N, and S2N- and the ionization potential, electron affinity, and vertical electronic spectrum of S2N. At the highest level of theory (estimated full CI or FCI), S2N+ is predicted to have a linear structure with r(N—S) = 1.51 Å. For S2N and S2N-, the minimum in energy at the FCI level corresponds to a quasi-linear [with a barrier height to linearity of about 2.0 kcal mol-1, ] and a bent structure , respectively. The adiabatic/vertical ionization potential and electron affinity of S2N are predicted to be 7.26/7.82 and 1.60/0.79 eV, respectively. Of the several electronic transitions in S2N considered, the ones with the excitation energy of 1.87 eV (X2 A1 → 2B2) and 2.87 eV (X2A1 → 2B2) are somewhat intense (ƒ = 0.005 and 0.002) and likely to be observed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 23 (1992), S. 239-248 
    ISSN: 1434-6079
    Keywords: 31.20.Tz ; 31.50. + w ; 33.10. − n ; 33.20.Rm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Multi-reference configuration interaction calculations of low-lying resonantK-shell excitations in the energy range below theK-shell ionization threshold have been performed for silane and mono-fluoro-silane. The calculated vertical transition energies are compared to experimentalK-shell photoabsorption spectra recorded by use of synchrotron radiation. The general structure and the intensity ratios of the experimental spectra are reproduced quite well by the present calculations; an assignment of the most prominent spectral features is undertaken. Correlations between the lowest dipole-allowedK-shell excitations of silane and mono-fluorosilane can be recognized.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 24 (1992), S. 177-198 
    ISSN: 1434-6079
    Keywords: 31.20.Di ; 33.10. - n
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A purely ab initio study of the vibronic structure of the C2H spectrum in the region up to 7000 cm−1, which is complicated by the coupling of theX 2Σ+ andA 2 II systems, is presented. The potential surfaces for the three lowest-lying electronic states 12 A′, 22 A′ and 12 A″ correlating withX 2Σ+ andA 2 II at the linear molecular geometry are calculated for the various geometrical distortions by means of the multireference configuration interaction (MRD-CI) method. These adiabatic surfaces are transformed into suitable diabatic counterparts. An approach is developed for a simultaneous treatment of three electronic states coupled via the bending and C-C stretching vibrations. Spin-orbit splitting of the vibronic levels and the vibronically averaged values for the hyperfine coupling constants are computed. The results obtained in this study enable a reliable explanation of the available experimental findings of the C2H spectrum and predict a number of features to be verified by future experiments.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 43 (1992), S. 659-668 
    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 definition of so-called first-order properties is, in general, not unique for approximate solutions of the Schrödinger equation. In the present work, the determination of molecular properties as the expectation value or energy derivative are compared for a wide class of electron correlation treatments that are based on the stationarity of certain modified energy functionals. The case in which all perturbation-dependent parameters in the energy expression are optimized is taken as a reference point, to which the derivative and the expectation value approaches are related by a sequence of approximations. By analyzing the validity of these approximations, we are in a position to give general criteria for the choice of the method to be employed. The derivative approach is shown to be a special case of a general method to improve the calculation of molecular properties. Furthermore, this method is extended to give a correction to the energy itself. © 1992 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
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