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  • 1
    Electronic Resource
    Electronic Resource
    Ab initio study of cis-butadiene valence and Rydberg states using the effective valence shell Hamiltonian method (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 3260-3275 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Low-lying σ- and π-electron vertical excitation energies of s-cis-1,3-butadiene are calculated using the ab initio effective valence shell Hamiltonian (Hv) method. The only experimentally known vertical excitation energy is that to the 1 1B2 state at 5.49 eV, while the Hv computation in the π-valence space yields 5.62 eV. Calculated excitation energies to various valence and Rydberg states are in good agreement with theoretical multiconfigurational single reference state second-order perturbation theory calculations by Roos and co-workers and with values from other highly correlated computations. The Hv calculations for cis-butadiene further investigate the dependence of the computations on the nature and the choice of molecular orbitals and provide the first comprehensive study of the convergence with respect to the enlargement of the valence space for π-electron systems. The present computations also represent the first Hv treatment of the σ→π* and π→σ* excited states in conjugated π-electron systems, along with an analysis of the required degree of σ–π correlation within the valence (or reference) space. Vertical π-and σ-ionization potentials are also produced as a byproduct of the Hv calculations for neutral cis-butadiene, providing the first predictions of these ionization energies. The computations conclusively reconfirm the high accuracy of the Hv method. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471091
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  • 2
    Electronic Resource
    Electronic Resource
    Kramers' unrestricted Hartree-Fock and second-order Møller-Plesset perturbation methods using relativistic effective core potentials with spin-orbit operators: Test calculations for HI and CH3I (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 66 (1998), S. 91-98 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Kramers' restricted Hartree-Fock (KRHF) and second-order Møller-Plesset perturbation (KRMP2) methods using relativistic effective core potentials (RECP) with spin-orbit operators and two-component spinors are extended to the unrestricted forms, KUHF and KUMP2. As in the conventional unrestricted methods, the KUHF and KUMP2 methods are capable of qualitatively describing the bond breaking for a single bond. As a result, it is possible to estimate spin-orbit effects along the dissociation curve at the HF and MP2 levels of theory as is demonstrated by the test calculations on the ground states of HI and CH3I. Since the energy lowering due to spin-orbit interactions is larger for the I atom than for the closed-shell molecules, dissociation energies are reduced and bond lengths are slightly elongated by the inclusion of the spin-orbit interactions.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 91-98, 1998
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 3
    Electronic Resource
    Electronic Resource
    Spin-orbit effects on structures of closed-shell polyatomic molecules containing heavy atoms calculated by two-component Hartree-Fock method (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 1526-1533 
    Details
    ISSN: 0192-8651
    Keywords: geometry optimization ; spin-orbit effect ; two-component calculation ; effective core potential with one-electron spin-orbit operator ; photoelectron spectra ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We have implemented geometry optimization using an analytic gradient to a two-component Kramers' restricted Hartree-Fock (KRHF) method for polyatomic molecules with closed-shell configurations. The KRHF method is a Hartree-Fock method based on relativistic effective core potentials with effective spin-orbit operators. The derivatives of spin-orbit integrals are obtained by numerical differentiation. Geometries for the various forms of polyatomic hydrides containing row 6 p-block elements are optimized with and without spin-orbit interactions. The structural changes due to spin-orbit interactions are small, but show definite trends, which correlate well with the p1/2 spinor population. Atomization energies are reduced significantly by incorporating spin-orbit interactions for all molecules considered. The KRHF calculations of several methylhalides demonstrate that the spinor energies from the KRHF method can be useful for the interpretation of experimental photoelectron spectra of molecules exhibiting spin-orbit splittings.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 1526-1533, 1998
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 4
    Electronic Resource
    Electronic Resource
    Kramers' restricted hartree - fock method for polyatomic molecules using ab initio relativistic effective core potentials with spin - orbit operators (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 13 (1992), S. 595-601 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A two-component Kramers' restricted Hartree-Fock method (KRHF) has been developed for the polyatomic molecules with closed shell configurations. The present KRHF program utilizes the relativistic effective core potentials with spin-orbit operators at the Hartree-Fock (HF) level and produces molecular spinors obeying the double group symmetry. The KRHF program enables the variational calculation of spin-orbit interactions at the HF level. KRHF calculations have been performed for the HX, X2, XY(X, Y = I, Br), and CH3I molecules. It is demonstrated that the orbital energies from KRHF calculations are useful for the interpretation of spin-orbit splittings in photoelectron spectra. In all molecules studied, bond lengths are only slightly expanded, harmonic vibrational frequencies are reduced, and bond energies are significantly decreased by the spin-orbit interactions.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540130509
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    Paper (German National Licenses)
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