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  • 1
    Electronic Resource
    Electronic Resource
    The open-shell coupled-cluster method: Excitation energies and ionization potentials of H2O (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 467-471 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The open-shell coupled cluster method is used to calculate directly several electronic excitation energies and ionization potentials of the water molecule. Correlation effects are included by summing single and double virtual excitations to infinite order. Triple excitations are treated approximately, to the lowest order they appear. Their contribution is significant, 0.2–0.4 eV for excitation energies and 0.5–0.7 eV for ionization potentials. The calculated energies are in good agreement (∼0.15 eV) with experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453592
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  • 2
    Electronic Resource
    Electronic Resource
    N2 excitations below 15 eV by the multireference coupled-cluster method (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 3680-3682 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The multireference coupled-cluster method with singles and doubles is applied to the vertical excitations of N2 at R=2.074 bohr. Both valence- and Rydberg-type excitations are calculated, using an appropriate basis and rather large model spaces. Thirty-five excitations below 15 eV are reported and classified. Sixteen energies could be compared with experiment, and the average error was 0.13 eV. Good ionization potentials are also obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457824
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  • 3
    Electronic Resource
    Electronic Resource
    Multireference coupled cluster and multireference configuration interaction studies of the potential surfaces for deprotonation of NH+4 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 6395-6400 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Protonation/deprotonation reactions are represented by H++B(arrow-right-and-left)HB+. The ionization potential of H (13.6 eV) is higher than that of B for organic and most inorganic molecules (it is 10.166 eV for NH3), and the separated pair H+B+ will be lower in energy than the closed-shell pair H++B. The reaction path involves, therefore, an avoided crossing, and its theoretical study requires multideterminant methods. The reaction with B=NH3 (or R1R2R3N) is of interest in several fields, and its study is described here. The multireference coupled-cluster method (MR-CCM) and multireference double-excitation configuration interaction (MRD-CI) were used. At each (H3N---H)+ separation, from 1 to 11 bohr, the ground state MRD-CI energy was optimized with respect to the angle θ between the NH bond in the NH3 group and the C3 axis; MR-CCM and MRD-CI calculations were performed for the two lowest 1A1 states and the lowest 3A1. Two different reference determinants had to be used for the MR-CCM calculations at different regions, but this created no difficulties and the transition was smooth. Close agreement (a few mhartree) was obtained between MRD-CI and MR-CCM results. The avoided crossing, near R(H3N---H)+=4 bohr, is manifested by the rapid change in the CI and coupled-cluster method (CCM) mixing coefficients and by the transition of the NH3 group from pyramidal at small R to planar at large R. The lowest 1A1 state dissociates adiabatically to NH+3(2A1)+H(2S), whereas the single determinant self-consistent field (SCF) function dissociates to NH3(1A1)+H+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456305
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  • 4
    Electronic Resource
    Electronic Resource
    The open-shell coupled-cluster method: Effect of single excitations on electronic transition energies (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5248-5249 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ionization potentials (IP) of H2O and alkali atoms, excitation energies (EE) of H2O, and electron affinities (EA) of alkalies are calculated by the open-shell coupled-cluster method with double excitations only (CCD). Comparison with previously reported computations including single and double excitations (CCSD) gives the contributions of the singles. These are very small (0.02 eV) for alkali atom IPs, larger (up to 0.09 eV, or 20%) for alkali EAs, and about 0.2 eV for the water molecule IPs and EEs. One-half of the effect in water is assigned to single excitations from the closed shells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454580
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  • 5
    Electronic Resource
    Electronic Resource
    The open-shell coupled-cluster method in general model space: Five states of LiH (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 956-958 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The open-shell coupled-cluster method is used to calculate the potential functions of the five lowest states of LiH, at internuclear separation of 2.0≤R≤10.0 bohr, with a 18σ9π2δ basis. The usual complete-model-space calculation diverges, and a general, incomplete model space, comprising the physically important 2σ 2, 2σ3σ, and 2σ1π configurations (but excluding the high-energy determinants 3σ 2 and 1π 2 from the P space) is used. Good agreement with experimental molecular constants is obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455164
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  • 6
    Electronic Resource
    Electronic Resource
    The open-shell coupled-cluster method: Ionization potentials and electron affinities of the alkali atoms, Li to Cs (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 4693-4695 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The open-shell coupled-cluster method with single and double excitations (CCSD) is applied to the alkali atoms, Li to Cs, with moderately large basis sets. The calculated electron affinities are all within 0.01 eV of experiment, with valence-shell correlation contributing almost all the correction to the (poor) Hartree–Fock results. Errors in the 2S ionization potentials range from 0.02 (Li) to 0.22 eV (Cs); with relativistic corrections estimated from numerical Hartree–Fock, IPs are within 0.1 eV of experiment. 2P IPs are even more accurate (0.02–0.04 eV).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452832
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  • 7
    Electronic Resource
    Electronic Resource
    An electrostatic model for the energetics of large heterocluster cations (1992)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 96 (1992), S. 1569-1575 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100183a016
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  • 8
    Electronic Resource
    Electronic Resource
    Transition energies of lanthanum, actinium, and eka-actinium (element 121) (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 3954-3958 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The relativistic coupled cluster method is applied to the transition energies (ionization potentials, excitation energies, electron affinities) of lanthanum, actinium, and eka-actinium (element 121) in several ionization states. Good agreement with available experimental data is obtained. Large relativistic effects are observed for all three atoms, with transition energies changing by up to 2.5 eV even for the relatively light La. The first ionization potential of La is reduced from 7.135 to 5.582 eV (the experimental value is 5.577 eV). In Ac, the 7s shell is occupied before 6d, yielding 7s and 7s2 ground states for Ac2+ and Ac+, respectively, instead of the 5d and 5d2 states for the La ions. The ground state of E121 is 8s28p, to be compared with the ns2(n−1)d configurations of the lighter group-3 elements. The Breit effect on transition energies is significant (0.06–0.1 eV) for states including f orbitals and small (below 0.02 eV) for others. The contribution of virtual i orbitals (l=6) shows similar behavior. The electron affinities are predicted at 0.33 eV for La, 0.35 eV for Ac, and 0.57 eV for E121. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476995
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  • 9
    Electronic Resource
    Electronic Resource
    The relativistic Fock-space coupled-cluster method for molecules: CdH and its ions (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 3409-3415 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The relativistic coupled-cluster method starts from the Dirac–Coulomb–Breit Hamiltonian in its low-frequency approximation and includes correlation by Fock-space coupled-cluster with single and double excitations. One- and two-component approximations using the Douglas–Kroll transformation are also tested. Significant relativistic effects are found for CdH, with bond length contracting from 1.820 to 1.778 Å (experimental 1.781 Å) and binding energies decreasing from 0.87 to 0.70 eV (experimental 0.68 eV). The binding energy of the cation increases by 0.1 eV upon inclusion of relativity. The electron affinity of the molecule is 0.44 eV. The Douglas–Kroll values include nearly all the relativistic correction. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475740
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  • 10
    Electronic Resource
    Electronic Resource
    Quasidegenerate perturbation theory (1982)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 86 (1982), S. 2133-2140 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100209a005
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