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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 504-512 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio methods were applied to compute the potential curves for the X 3Σ− and A 3Π states, the transition dipole moment, and the radiative lifetimes of the vibrational levels of the A state of the SO molecule. Extended atomic natural orbital basis sets including up to g-type functions were used. The potential energy curves were computed at the multireference configuration interaction level of approximation. The calculated bond distances and bond energies are 1.498 (1.481) A(ring) and 5.21 (5.36) eV, respectively, for the X state, and 1.694 (1.609) A(ring) and 0.57 (0.64) eV, respectively, for the A state (experimental values within parentheses). Restricted active space self-consistent field (RASSCF) wave functions were used to obtain the transition dipole moments, and the size of the RASSCF active orbital space was increased until stability of the transition moment value was achieved. The calculated transition moment strongly depends on the internuclear distance. The calculated value of the A 3Π, v=0 lifetime is 46.6 μs, while the experimental values are in the range of 36–39 μs. The computed lifetime is a very sensitive function of the relative accuracy of the potential energy and transition moment curves: for example, removing the g-type function on sulphur increases the lifetime to 55 μs.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 3063-3070 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The multiconfigurational time-dependent Hartree–Fock (MCTDHF) method is used to study the excitation energies and transition moments of the CH+ ion. A consistent approach to the selection of configurations based on the complete active space (CAS) model is successfully applied. In this approach a large set of orbitals is included in the active space without a substantial increase in the number of configurations, since only for a smaller subset of orbitals is the configuration expansion complete and the remaining orbitals active are considered an auxiliary set. For CH+ the active space includes the valence and additional orbitals, with the valence orbitals constituting the complete subset. Extra configurations involving single and double excitations from the valence to the additional (auxiliary) orbitals are included both for the MCSCF reference state and in the MCTDHF. It is demonstrated that this active space accurately mimics MCSCF and MCTDHF calculations with an enlarged complete active space which includes both the original CAS and the auxiliary orbitals. The calculations for the 1 Π and 1 Σ+ excited states at the equilibrium geometry show that accurate excitation energies and transition moments are obtained in this way. For most of these states for which there are other good ab initio results available, we obtain comparable excitation energies and transition moments. In addition to 1 Π and 1 Σ+ , low lying states of other symmetries are obtained and discussed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7229-7235 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio calculations have been performed for the static and dynamic polarizability and hyperpolarizability for a series of polyynes C2nH2 using self-consistent field (SCF) (n=1–6) and multiconfiguration self-consistent field (MCSCF) (n=1–4) wave functions. We have considered the longitudinal component of the static hyperpolarizability and the same component of the dynamic hyperpolarizability measured in electric-field induced second harmonic generation γESHG=γ(−2ω;ω,ω,0). The frequency dependence of the polarizability and hyperpolarizability has been rationalized in terms of the coefficients in expansions in ω2. The static hyperpolarizabilities vary smoothly with the chain length and satisfy γ(C2nH2)=γ (C2H2)×nX, where X≈3.0. The dynamic hyperpolarizability satisfies a similar relation where X increases slowly with ω.
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  • 4
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Multiconfigurational self-consistent field (MCSCF) response is used to study the electric field dependence of magnetizabilities and nuclear shielding constants for N2, C2H2, HCN, and H2O. London perturbation-dependent atomic orbitals are used to ensure gauge origin independence. The computed magnetizabilities and shielding derivatives show a strong electron correlation dependence. The N2 results confirm the conclusions of previous ab initio studies. For the other molecules, this is the first study of the above magnetic properties beyond the SCF approximation. © 1995 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 71-72 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effect of the interatomic interaction on the static dipole polarizability has been reexamined in detail for the He dimer at the equilibrium internuclear distance of RHe... He=5.6 a0 by using high-precision explicitly correlated R12 approaches. Our most accurate CCSD(T)-R12 results for the increments of the polarizability are 61.79×10−3 a.u. for the anisotropy and −1.04×10−3 a.u. for the trace, not significantly different from recent literature CCSD data and confirming their high accuracy. © 2000 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 99 (1977), S. 4624-4628 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5652-5659 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The coupling of the intermolecular interaction with the intramolecular correlation effects is considered using the coupled cluster (CC) formalism. The CC equations for the dispersion energy are presented and their relation to the double perturbation theory is analyzed. An approximate scheme based on partial decoupling of the CC equations is applied for the He–He interaction. Numerical results are obtained using explicitly correlated Gaussian geminal basis set. They confirm the importance of the intraatomic (apparent) correlation effects and agree very well with the experimentally derived potential.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 48 (1978), S. 323-329 
    ISSN: 1432-2234
    Keywords: BH, magnetic susceptibility of ∼
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The coupled Hartree-Fock (CHF) perturbation approach and its extension to multiconfiguration wavefunctions (MC CHF scheme) were used to calculate the magnetic susceptibility of the BH molecule. The results obtained for an SCF and two pair-excitation MC SCF functions confirm the paramagnetism of the BH molecule and indicate a rather weak dependence of the computed molecular susceptibility on the correlation effects.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 48 (1978), S. 323-329 
    ISSN: 1432-2234
    Keywords: BH, magnetic susceptibility of ∼
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The coupled Hartree-Fock (CHF) perturbation approach and its extension to multiconfiguration wavefunctions (MC CHF scheme) were used to calculate the magnetic susceptibility of the BH molecule. The results obtained for an SCF and two pair-excitation MC SCF functions confirm the paramagnetism of the BH molecule and indicate a rather weak dependence of the computed molecular susceptibility on the correlation effects.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 71 (1987), S. 375-384 
    ISSN: 1432-2234
    Keywords: MCSCF ; Correlation ; Effective potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A method is suggested which allows the inclusion of dynamic correlation into CASSCF calculations. An effective Coulomb hole potential is added to the Hamiltonian. The potential has a simple form, which allows its implementation into existing LCAO programs using Gaussian integral packages. The parameters appearing in the potential are determined by fitting to empirical valence correlation energies for first row atoms. Calculations of ionization energies and electron affinities show considerable improvement compared to the MCSCF values. Test calculations on three molecules give the following results, H2∶ r e=0.745 (0.741) Å, D e=4.62 (4.75) eV; N2∶ r e=1.099 (1.098) Å, D e= 10.42 (9.91) eV; O2∶ r e=1.198 (1.207) Å, D e=4.73 (5.21) eV. Experimental values within parenthesis.
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