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  • 1985-1989  (3)
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  • 1
    Electronic Resource
    Electronic Resource
    Charge distributions and valency in copper oxide crystals related to superconductivity (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 2983-2992 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present an overview of the discrete variational method for calculating orbital states of a molecular cluster in the local density approximation. Then we introduce a new method of embedding a finite molecular cluster in a crystal lattice. This new technique of cluster weighting is based on the bulk stoichiometry of the crystal and the Mulliken populations for chemically complete atoms—those atoms that have all their covalently bonded nearest neighboring atoms also in the cluster. We have applied our new approach to calculate linear-combination-of-atomic-orbitals ground states for seven copper oxide crystals and Cu metal. The average net Mulliken charges calculated for Cu atoms in this way are shown to correlate well with the observed energies of the Cu K edge feature in x-ray absorption spectra of these materials. Several of these compounds are important to understanding the high Tc superconductivity of copper oxides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456919
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    A systematic analysis of the spectra of the lanthanides doped into single crystal LaF3 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3443-3457 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The optical spectra of the lanthanides doped into single crystal LaF3 have been interpreted in terms of transitions within 4f N configurations. Energy matrices combining free-ion terms with a crystal field for an approximate model which assumes C2v instead of the actual C2 site symmetry were diagonalized. Excellent correlations were obtained between experimental transition energies and the computed level structures. We also report the results of previously unpublished experimental spectroscopic investigations of Nd3+ and Sm3+:LaF3, as well as predicted energy levels for Pm3+:LaF3. The spectroscopic data for each ion were independently interpreted using an effective-operator model, then the model parameters were intercompared. Systematic trends have been identified, and a comprehensive energy level diagram is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455853
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Neutron inelastic experiments on actinide dioxides: Search for crystal-field levels in NpO2 (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3598-3600 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Early experiments at the pulsed neutron source at Argonne National Laboratory (ANL) showed that it was possible to observe crystal-field (CF) levels at energy transfers above 150 meV in UO2. More recent investigations at the UK pulsed source at Rutherford Laboratory have improved the resolution and seen a series of well-resolved peaks. Based on these measurements the CF parameters are V4=−130 meV and V6=+30 meV. Since these parameters should be independent of the precise An ion, there is interest in looking at the tetravalent oxides UO2, NpO2, and PuO2. We have now performed experiments at ANL on NpO2 at temperatures between 15 and 200 K. We find no sharp peak in the excitation spectrum up to energy transfers of about 250 meV. This result is contrary to the expected strong transition at about 53 meV using the above CF parameters in a complete intermediate coupling calculation. The observed phonon spectrum of NpO2, in comparison with that of ThO2, shows larger widths in all of the three vibrational bands above ∼30 meV, which may indicate strong interaction between CF levels with optic phonons in NpO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340706
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    Paper (German National Licenses)
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