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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Charge transfer excitations in the photoelectron spectrum of Cl−NH3: Experiment and calculation (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 6201-6204 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A charge transfer (CT) excited state has been identified in the photoelectron spectrum of Cl−NH3. A narrow band at 4.0 eV binding energy (BE) is assigned to ionization of Cl−, and a broad band peaking at 6.45±0.15 eV BE corresponds to a CT state, Cl−NH+3. The assignments are confirmed by ab initio calculations, yielding binding energies of 3.88 and 6.36 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465913
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  • 6
    Electronic Resource
    Electronic Resource
    The Fock-space coupled-cluster method: Electron affinities of the five halogen elements with consideration of triple excitations (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 6773-6776 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Fock-space coupled-cluster method with single and double excitations (CCSD or SUB2) is applied to the calculation of the electron affinities of all five halogen elements, F–At. Excellent agreement with experiment is obtained, the average error being 0.04 eV. The inclusion of triple excitations for F and Cl spoils the agreement. Comparison with other methods is made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465820
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  • 7
    Electronic Resource
    Electronic Resource
    Degeneracy breaking in the Hilbert-space coupled cluster method (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 3090-3094 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Hilbert space multireference coupled cluster method with single and double excitations (HS–MRCCSD) is applied to excited states of the N2 molecule. Particular attention is given to the breaking of degeneracy, where sublevels which should be degenerate by symmetry come out separated by as much as 0.3 eV. This feature is explained by the fact that a truncated coupled cluster expansion starting from an open-shell determinant does not preserve spin or spatial symmetry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464135
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  • 8
    Electronic Resource
    Electronic Resource
    Ground and excited states of K2 and K2+ by the open-shell coupled cluster method (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7126-7131 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Fock space open-shell coupled cluster method is used to calculate the potential functions of the five lowest states of K2 at internuclear separation of 2≤R≤7 A(ring) and the three lowest states of K2+ at 2≤R≤15 A(ring), with a 112-function contracted Gaussian basis. The usual complete-model-space calculation diverges and a general, incomplete model space is used. Core and core–valence correlation is found to be important, and very good agreement with experimentally known molecular spectroscopic constants is obtained when it is included: equilibrium internuclear separations (except for the very flat x 3Σu+ state of K2) are accurate to 0.07 A(ring), dissociation and excitation energies to 0.09 eV, and vibrational constants to 6 cm−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465097
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  • 9
    Electronic Resource
    Electronic Resource
    The relativistic open shell coupled cluster method: Direct calculation of excitation energies in the Ne atom (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 8455-8458 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The relativistic Fock space coupled-cluster method for the direct calculation of excitation energies (including fine structure) is presented and applied to excitations of atomic Ne. The coupled clusters with single and double excitations (CCSD) approximation, which includes single and double virtual excitations in a self-consistent manner, is implemented. The no-pair Dirac–Coulomb Hamiltonian is taken as the starting point. Mean length basis sets of balanced Gaussian spinors are used to span the atomic orbitals. The model (P) space is quasicomplete, consisting of determinants with one valence hole and one valence particle. Fourteen excitation energies of the atom are calculated. They all agree with experiment to 0.08 eV or better, with an average error of 0.02 eV. Fine structure splittings are also in very good agreement with experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463416
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  • 10
    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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