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  • 1
    Electronic Resource
    Electronic Resource
    Molecular orbital calculations on the nitrogen nuclear spin-spin coupling constants (1975)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 79 (1975), S. 1863-1867 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100584a022
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  • 2
    Electronic Resource
    Electronic Resource
    Hydride-transfer reactions: temperature dependence of rate constants for isopropyl(1+) + isobutane = propane + tert-butyl(1+); clusters of isopropyl(1+) and tert-butyl(1+) with propane and isobutane (1989)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 93 (1989), S. 4010-4016 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100347a030
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  • 3
    Electronic Resource
    Electronic Resource
    Density functional studies of UO22+ and AnF6 (An=U, Np, and Pu) using scalar-relativistic effective core potentials (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 7345-7350 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have performed one-component relativistic calculations to determine the bond lengths and harmonic vibrational frequencies of UO22+ and AnF6 (An=U, Np, and Pu) using various density functional calculations with relativistic effective core potentials (RECPs) and extended basis sets. The calculated spectroscopic constants using small-core RECPs compare favorably with the available all-electron relativistic results for UO22+ and UF6. The results using the hybrid functionals are in very good agreement with the experimental data for the geometries and vibrational frequencies of the AnF6 systems. The performance of pure gradient-corrected functionals is poor, even worse than that of local density functional for the geometries and vibrational frequencies. For the vibrational frequencies, the hybrid functional calculations give qualitatively the correct order with small quantitative deviations from the experimental data. The local density functional provides reliable frequencies for the stretching modes but underestimates the frequencies for the bending modes. The pure gradient-corrected functionals underestimate the frequencies for all the stretching and bending modes. While the large-core RECP calculations provide short bond lengths and a rather poor description for vibrational frequencies relative to small-core RECP calculations for UO22+ and UF6, they may still be a practical choice of method provided hybrid functionals are also used, especially for larger systems. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1312827
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  • 4
    Electronic Resource
    Electronic Resource
    Approaches to bifurcating reaction path (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 1933-1939 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The intrinsic reaction path (IRP) often becomes unstable relative to some nontotally symmetric direction orthogonal to the path through a valley–ridge inflection point. We investigate geometric characters of the potential energy surface around the valley–ridge inflection boundary, and propose some ideas to determine a bifurcating reaction path, or to give a two-dimensional potential energy surface which connects bifurcating point and product regions. As a demonstration, bifurcating reaction paths are calculated for the isomerization reaction of methoxy radical (H3CO→H2COH) by the unrestricted Hartree–Fock (UHF) method. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472063
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  • 5
    Electronic Resource
    Electronic Resource
    A complete active space valence bond (CASVB) method (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 9227-9239 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A complete active space valence bond (CASVB) method is proposed which is particularly adapted to chemical interpretation. A CASVB wave function can be obtained simply by transforming a canonical CASSCF function and readily interpreted in terms of the well known classical VB resonance structures. The method is applied to the ground and excited states of benzene, butadiene, and the ground state of methane. The CASVB affords a clear view of the wave functions for the various states. The electronic excitation is represented in a VB picture as rearrangements of the spin couplings or as charge transfers which involve breaking covalent bonds and forming new ionic bonds. The former gives rise to covalent excited states and the latter to ionic excited states. The physical reasons why it is so difficult to describe the ionic excited states at the CASSCF level with a single active space and why the lowest 1 1B+2 state in cis-butadiene is so stabilized compared to the corresponding 1 1B+u state in the trans isomer are easily identified in view of a VB picture. The CASVB forms a useful bridge from molecular orbital theory to the familiar concepts of chemists. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472754
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  • 6
    Electronic Resource
    Electronic Resource
    On the performance of diagrammatic complete active space perturbation theory (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 7773-7778 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Excited states of C2, H2O, CO, and formamide are studied to illustrate the performance and accuracy of second-order diagrammatic complete active space perturbation theory (D-CASPT2) [J. Chem. Phys. 108, 1081 (1998)]. Comparisons are made with other ab initio methods and also full configuration interaction (FCI) calculations or experiment. Excitation energies computed by the D-CASPT2 method are quite accurate showing an average deviation of 0.1 eV from the FCI values for C2 and H2O. The CO and formamide excitation energies yield average deviations of 0.1 and 0.2 eV from experiment, respectively. The computational cost of this method is reduced to a great extent compared to the MRMP method. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1316044
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  • 7
    Electronic Resource
    Electronic Resource
    The higher-order Douglas–Kroll transformation (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 7786-7789 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The higher-order Douglas–Kroll (DK) Hamiltonians in an external potential are explicitly derived. Application of an exponential-type unitary operator with the 2n+1 rule significantly simplifies the formulations of the high-order DK Hamiltonians. The third-order DK method has been implemented practically. Numerical results for one- and many-electron systems show that good accuracy can be obtained even with the DK Hamiltonian correct to third order in the external potential. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1316037
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  • 8
    Electronic Resource
    Electronic Resource
    Relativistic and correlated all-electron calculations on the ground and excited states of AgH and AuH (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 8015-8025 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report relativistic all-electron multireference based perturbation calculations on the low-lying excited states of gold and silver hydrides. For AuH, we consider all molecular states dissociating to the Au(2S)+H(2S) and Au(2D)+H(2S) atomic limits, and for AgH, the states corresponding to the Ag(2S)+H(2S), Ag(2P)+H(2S), and Ag(2D)+H(2S) dissociation channels. Spin-free relativistic effects and the correlation effects are treated on the same footing through the relativistic scheme of eliminating small components (RESC). Spin–orbit effects are included perturbatively. The calculated potential energy curves for AgH are the first reported in the literature. The computed spectroscopic properties agree well with experimental findings; however, the assignment of states does not correspond to our calculations. Therefore, we give a reinterpretation of the experimentally observed C 1Π, a 3Π, B 1Σ+, b(3Δ1)1, D 1Π, c13Π1, and c0(3Π0) states. A labeling suggested by us is a1, C0+, b0−, c2, B3Π0+, d3Π1, e1, f1 and g1, respectively. The spin–orbit states corresponding to Ag(2D)+H(2S) have not well defined the Λ and S quantum numbers, and therefore, they probably correspond to Hund's coupling case c. For AuH, we present a comparison of the calculated potential energy curves and spectroscopic parameters with the previous configuration interaction study and the experiment. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1308554
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  • 9
    Electronic Resource
    Electronic Resource
    Structure and stability of Na6Pb clusters (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 6613-6617 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The geometric and electronic structures of the bimetallic cluster, Na6Pb, have been calculated using the density functional and coupled-cluster approaches, with a relativistic effective core potential and one-electron spin–orbit operators. Six possible isomeric Na6Pb structures (Oh, D3h, D3d, C5v, C3v, and C2v) have been examined, and the highly symmetrical Oh structure was found to be the most stable form. The stabilities of the clusters correlate well with the Pb–Na bond distances and with the charge transfer from the Na6 subsystem to the more electronegative Pb atom. The binding energies were found to vary according to the structure, with a spread of about 0.1 eV and 0.3 eV for the density functional and coupled-cluster calculations, respectively. These are of the same order, and somewhat smaller, as are found for the Na6Mg clusters (about 0.5 eV), demonstrating that the stabilization of the Na6Pb cluster is not particularly dependent on the geometric structures. At the same time, we found that the Na6Pb cluster is more stable as the symmetry is higher. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1311298
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  • 10
    Electronic Resource
    Electronic Resource
    Theoretical study of the excitation spectra of five-membered ring compounds: Cyclopentadiene, furan, and pyrrole (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 2312-2320 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Multireference perturbation theory with complete active space self-consistent field (CASSCF) reference functions was applied to the study of the valence and Rydberg excited states in the range of 5–8 eV of five-membered ring compounds, cyclopentadiene, furan, and pyrrole. The spectra of these molecules have been studied extensively for many years but characterization is far from complete. The present approach can describe all kinds of excited states with the same accuracy. The calculated transition energies are in good agreement with corresponding experimental data. We were able to predict the valence and Rydberg excited states with an accuracy of 0.27 eV or better except for the B+2 of pyrrole. The valence excited states of five-membered ring compounds were interpreted in terms of the covalent minus states and ionic plus states of the alternate symmetry. The unobserved 1A1→A−1 transition with very weak intensity, which is hidden under the strong 1A1→B+2 transition, is also discussed. Overall, the present theory supports the assignments recently made by Serrano-Andres et al. based on the CASSCF plus second-order perturbation results. However, there remain some discrepancies in the assignment of the spectrum of pyrrole. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470926
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