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  • 1
    Electronic Resource
    Electronic Resource
    Ab initio quantum chemical study of the .pi.-electron spectrum of the cytosine molecule (1988)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 110 (1988), S. 7664-7671 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00231a014
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  • 2
    Electronic Resource
    Electronic Resource
    A CASSCF study of the potential curves for the X 1Σ+, A 1Π, and C 1Σ+ states of the AlH molecule (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5032-5042 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The complete active space SCF (CASSCF) method was applied to compute the potential curves for the X 1Σ+, A 1Π, and C 1Σ+ states of the AlH molecule. Molecular constants were obtained from the potential curves by solving the radial Schrödinger equation. The results obtained for the ground state are in excellent agreement with experiment, and show that the intershell correlation effects only have a very small effect on the properties of AlH. Calculated values for ΔGv+1/2 differ from experiment within 4.4–5.6 cm−1for the five known band origins (v=0–4). The calculated dissociation energy (De) is 3.11 eV (experiment, 3.16 eV). The A state has a shallow minimum followed by a maximum. Two bound vibrational states have been found, the upper predissociative. The calculated value for De is 0.12 eV, which is 0.12 eV less than the experimental value. All deviations from experiment can be derived from this error. Rotational constants are in excellent agreement with experiment. Radiative lifetimes for the two bound states have been computed to be 62 (v=0) and 102 ns (v=1). The corresponding experimental values are 66±4 and 83±6 ns, respectively. The C state exhibits a double minimum in the potential curve, with the outer minimum lower in energy, in contrast to the corresponding state in BH.The dissociation energy (D0), 0.61 eV agrees well with the value 0.64 eV derived from experimental data. The second minimum is located at R=3.76 A(ring) and has a depth of 1.16 eV. Transition moments from the six lowest levels of the ground state to any of the outer minimum levels are all very small and this minimum is not expected to be seen in absorption. The rotational levels for the second vibrational band in the inner minimum are heavily perturbed by interaction with outer minimum levels, and a normal analysis of the spectrum in terms of Bv and Dv is not possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452679
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  • 3
    Electronic Resource
    Electronic Resource
    A CASSCF-CCI study of the valence and lower excited states of the benzene molecule (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 1458-1466 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio complete active space (CAS) SCF and contracted CI calculations have been carried out for all valence and the lower Rydberg states of the benzene molecule. The CASSCF active space comprised 12 π-type molecular orbitals and the basis set included both polarization functions and diffuse functions in order to describe properly both valence and Rydberg type orbitals. Resulting excitation energies for the Rydberg states are in close agreement with experiment. CASSCF results for the valence states give errors ranging from 0.0 for the covalent states up to more than 1.0 eV for the most ionic states. Inclusion of σ–π correlation effects reduces the errors in the ionic states to less than 0.6 eV. The 1E1u state is computed to lie 7.4 eV above the ground state with a transition moment of 1.70 a.u., experimental values are 7.0 eV and 1.61 a.u., respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452235
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  • 4
    Electronic Resource
    Electronic Resource
    A theoretical study of the A 1Π←X 1Σ+ system of SiH+ (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 423-432 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Theoretical studies have been performed on the X 1Σ+ and A 1Π states of SiH+. The complete active space, self-consistent field (CASSCF) and many-body perturbation theory (MBPT) methods were employed for the X 1Σ+ and state while the A 1Π excited state potential energy curve was studied by using CASSCF, multireference contracted configuration interaction (MR CCI, (MR CEPA), and coupled pair functional (CPF) approaches. Excellent agreement was obtained with experiment for the X state spectroscopic parameters (CASSCF): re=1.505 (1.50 A(ring); D0=3.30 (3.22±0.03) eV; ωe=2161 (2155) cm−1; ΔG1/2=2093 (2089) cm−1, with experimental values within parentheses. The shape of the potential curve for the A state was very sensitive to the basis set and higher order electron correlation. The best results, obtained with the CPF method, were re=1.888 (1.871) A(ring); D0=0.15 (0.15±0.03) eV; ωe=438 (448) cm−1; ΔG1/2=318 (389) cm−1. The computed f0,0 oscillator strength for the A←X transition was 1.2×10−3 which falls between the laboratory value, (2.4±1)×10−3, and a value obtained from the solar spectrum, 0.5×10−3. The computed life time for the v'=0 state is 956 ns to be compared to the experimental value 1025±80 ns.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455483
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  • 5
    Electronic Resource
    Electronic Resource
    The extended Koopmans' theorem Fock operatorThis work is in part based on a thesis submitted by J. Mauricio O. Matos to the Department of Physics of the University of Ceará as a requisite to obtaining a master's degree. (1987)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 871-892 
    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: By expanding the wave function of a system of N particles in terms of products of functions of one and (N-1) particles, the one-particle, nonlocal operator F̂EKT (extended Koopmans' theorem) is determined. It is shown that although this operator is nonhermitian, its eigenvalues and eigenfunctions represent the ionization energies and occupied orbitals, respectively. The eigenfunctions of F̂EKT are the one-particle functions that enter into the expansion of the wave function of the system as partners of the (N-1)-particle wave functions. The eingenvalues are also one-particle energies that, multipled by the orbital occupancy probalities, enter the expression for the total N-particle energy of the system.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560310604
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