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  • 1990-1994  (6)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Spin fluctuations and covalence in neutron Bragg scattering from YBa2Cu3O6 and La2CuO4 : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5382-5384 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A puzzle is pointed out concerning the low-temperature behavlor of La2CuO4 and YBa2Cu3O6, the insulating "parents'' of the high-Tc superconductors, and indicate a possible solution. The measured ordered magnetic moment is about 0.64 μB per Cu, in agreement with the value calculated on the basis of the Heisenberg Hamiltonian. But this calculation is within a nearly purely ionic or localized picture of the Cu d hole, the reduction from 1.1 μB (g≈2.2) being entirely due to spin fluctuations. Thus the almost perfect agreement leaves no room for the moment reduction due to covalence or 3d-2p hybridization, expected to be large in these oxides. A possible explanation might lie in the fact that an ostensibly symmetry-based argument relating the calculated moment (in the symmetry-unbroken state) to that measured is not valid, as has recently been shown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348039
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetism in the insulating parents of the high-Tc superconductors: Well or ill understood? : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6105-6107 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We discuss appreciable differences between the results for the covalent reduction of the ordered moment in antiferromagnetic CuO2 planes obtained by various groups, including the present authors. We explain the differences as due to differences in definition, the definition that we used being closely based on experiment (magnetic neutron Bragg scattering), in contrast to the others. We also discuss the large difference between the zero-point spin fluctuations as calculated by one of the groups and the well-known result of spin wave theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352715
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Electronic structure of Li(9-crown-3)2: A molecule with a Rydberg-type ground state (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 9758-9764 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report unrestricted Hartree–Fock (UHF) results for the molecule Li(9C3)2, obtained with several basis sets, including diffuse functions, up to 6-31G++**. These results show that (1) the spatial distribution of the highest occupied molecular orbital (HOMO), or valence, electron is predominantly "outside'' the Li(9C3)2 complex. That is, the complex is rather accurately described by the formula Li+(9C3)2e−; (2) the spin density at the Li nucleus drops by about three-orders of magnitude, as compared to the free lithium atom; (3) the character of the ground state, and the first few excited states, is predominantly Rydberg-type, centered on the lithium, with the valence electron "loosely'' bound to the complex. We argue that this complex is thermodynamically stable, and show graphically what happens to the spin density as the 9-crown-3 (9C3) molecules complex the neutral lithium atom. As far as we are aware, this is the first example of a neutral molecule with a Rydberg-type ground-state. We also discuss the relation of our results to the properties of the crystalline electrides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464354
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    On the electronic structure of electrides (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5875-5882 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We explore a mechanism for the remarkable charge isolation of the localized, or trapped, electrons found in the crystalline electrides Cs(18C6)2 and Cs(15C5)2. 133Cs NMR measurements show only ≈ 0.05% atomic character of the spin density at the Cs nucleus, consistent with many features of the structure and measured properties which indicate that the localized electron distribution is centered at the anion vacancies. The optical absorption data suggest that the localized electrons, which give rise to the Curie-law spin susceptibility, must penetrate appreciably into the crown ethers, (18C6) and (15C5), which encapsulate the Cs. We suggest that the large reduction of the spin density at the Cs nucleus is due to a Coulomb barrier resulting from negative charge on the oxygens. A crude model, one electron moving in two spherical charged shells surrounding the Cs core, illustrates the mechanism and accounts accurately for the ratio of spin densities at the Cs nucleus found in the 18C6 and the 15C5 electrides. Hartree–Fock calculations for an idealized model of an isolated Cs(18C6)2 molecule, namely Li(9C3)2, tend to support the mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459584
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Rydberg-like Ground States of H[111]-Cryptate and H2[111]-Cryptate: An ab Initio Study (1994)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 6967-6971 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100079a014
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    An ab Initio Investigation of [111]-Cryptates: Their Structure and Their Chemistry (1994)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 6972-6979 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100079a015
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    Paper (German National Licenses)
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