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  • 1
    Electronic Resource
    Electronic Resource
    A MCSCF study of homoaromaticity and the role of ion pairing in the stabilization of carbanions (1986)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 108 (1986), S. 6554-6561 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00281a019
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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    On the electronic structure and spectrum of CuF2 and CuCl2 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4785-4792 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ground and low-lying states of CuF2 and CuCl2 have been studied using the single and doubles configuration interaction (SDCI) and coupled pair functional (CPF) methods in a large Gaussian basis set including up to g-type functions. The results include a determination of the bond distances for all the ligand field states (the three states with one hole in the 3d shell) and charge transfer (CT) states, and force constants for the ligand field states. Overall the SDCI (with or without the Davidson correction for higher excitations) and CPF results are in good agreement. The CPF results, which we believe to be the most accurate, can be summarized as follows. The computed value for the asymmetric stretching frequency in the 2Σ+g ground state of CuF2 is 740 cm−1, compared to the experimental value of 765 cm−1. The d–d transition energies for CuF2 are 2500 and 10 800 cm−1. The two lowest charge transfer states are at 31 200 and 33 900 cm−1, respectively. CuCl2 has been found to have a ground state which is an almost equal mixture of 2Σ+g and 2Πg when an estimate of the spin–orbit interaction is included. Three d–d transitions are found: 1600 cm−1 ( J=1/2), 7500 cm−1 (J=3/2), and 9700 cm−1 (J=5/2). The lowest charge transfer states have been computed to lie at 16 700 and 19 600 cm−1. Two bands have been found in the gas-phase spectrum of CuCl2 at 9000 and 19 000 cm−1, in good agreement with the present results. The computed f value for the CT band is 0.017, to be compared to the experimental value of 0.014.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456716
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Determinant based configuration interaction algorithms for complete and restricted configuration interaction spaces (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 2185-2192 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A restricted active space (RAS) wave function is introduced, which encompasses many commonly used restricted CI expansions. A highly vectorized algorithm is developed for full CI and other RAS calculations. The algorithm is based on Slater determinants expressed as products of alphastrings and betastrings and lends itself to a matrix indexing C(Iα, Iβ ) of the CI vector. The major features are: (1) The intermediate summation over determinants is replaced by two intermediate summations over strings, the number of which is only the square root of the number of determinants. (2) Intermediate summations over strings outside the RAS CI space is avoided and RAS calculations are therefore almost as efficient as full CI calculations with the same number of determinants. (3) An additional simplification is devised for MS =0 states, halving the number of operations. For a case with all single and double replacements out from 415 206 Slater determinants yielding 1 136 838 Slater determinants each CI iteration takes 161 s on an IBM 3090/150(VF).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455063
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  • 6
    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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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Singlet and triplet potential surfaces for the nickel-ethylene [Ni(C2H4)] complex. A CASSCF-CI study (1985)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 89 (1985), S. 2180-2186 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100257a009
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  • 9
    Electronic Resource
    Electronic Resource
    The nature of the bonding in XCO for X=Fe, Ni, and Cu (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 354-364 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The bonding in the 5,3Σ− and 3Δ states of FeCO, the 3,1Σ+, 3Δ, and 3 Π states of NiCO, and the 2Σ+ state of CuCO are analyzed using the constrained space orbital variation (CSOV) technique for both (CASSCF) and SCF wave functions. The bonding is discussed in terms of σ repulsion between the metal 4s and the CO 5σ, CO to metal σ donation when there is an empty or partly occupied dσ orbital and metal to CO 2π * backdonation. The bonding is compared for the different metals and between the different states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451610
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  • 10
    Electronic Resource
    Electronic Resource
    An ab initio study of the molecular structure and vibration-rotation spectrum of the triplet radical HCCN (1988)
    Springer
    Theoretical chemistry accounts 73 (1988), S. 155-171 
    Details
    ISSN: 1432-2234
    Keywords: HCCN ; Vibration-rotation ; Potential energy surface
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The bent triplet cyanocarbene H-C-C≡N and the linear triplet allene H-C=C=N have been studied by the CASSCF and CI methods, using a DZP basis. Relaxation of all geometrical parameters for the CASSCF energy results in a bent molecule with CCH angle 133° and a barrier to linearity of 6.4 kcal/mol, which was lowered to 2.3 kcal/mol in a subsequent CI calculation. The Davidson correction lowered it further to 1.8 kcal/mol. A 26-term analytical potential energy surface (PES) was fitted to CASSCF, CI, and Davidson corrected CI energies in 94 different geometries. Using these three potentials, the semi-rigid bender model predicts a CCH bending frequency of 782, 505, and 503 cm−1, resp., which compares favourably with an experimentally observed IR transition line at 458 cm−1. For the deuterated species, the corresponding frequencies are 610, 407, and 402 cm−1, to be compared with two possible absorption lines at 405 and 317.5 cm−1. The PES was then parametrized by adding a variable CCH angle dependence, and a comprehensive vibration-rotation spectrum was calculated variationally, using the exact 4-atom vibration-rotation kinetic Hamiltonian, for a range of barrier heights. Comparison with experiment indicates a barrier in the range 1±0.5 kcal/mol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00528202
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