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'Electronic structure' in keywords Facet   Publication Year 1993  [X]
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1993[X]
1Author    Michael SpringborgRequires cookie*
 Title    A Comparison between Polyatecylene and Polycarbonitrile  
 Abstract    Results of a theoretical, comparative study of the electronic properties of trans-polyacetylene and polycarbonitrile are reported. Polyacetylene consists of zigzag chains of CH units, whereas poly-carbonitrile has every second CH unit replaced by an N atom. Ground-state properties (structure, electronic bonds and bands, densities of states, momentum distributions, and reciprocal form factors) of the periodic, infinite, isolated chains are studied by means of first-principles, density-functional calculations. It is demonstrated how the presence of the (nitrogen) heteroatoms in the backbone of polycarbonitrile leads to a partial localization of the electrons. In order to investigate charged chains, model calculations are subsequently performed. These indicate solitons but not polarons to be stable. In total, the analysis demonstrates how the combination of information that can be obtained from various experiments provides a detailed description of the compounds. 
  Reference    Z. Naturforsch. 48a, 159—164 (1993); received November 26 1991 
  Published    1993 
  Keywords    Conjugated polymers, Structure, Electronic structure, Momentum densities, Solitons 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0159.pdf 
 Identifier    ZNA-1993-48a-0159 
 Volume    48 
2Author    F. Gasser, M. RoethRequires cookie*
 Title    Compton Profiles for Atoms and Molecules: Compton Defects  
 Abstract    A series expansion applied to the Born propagator present in the differential cross-section allows one to obtain successive corrections to the impulse approximation. The first and second corrections explain the essential features of the Compton defects. Results for the second corrective term are presented for 1 s, 2 s, 2 p x , and 2 p z hydrogenic states. The decrease or increase of the scattered intensity near the maximum of the Compton profile is shown to be strongly related to geometric properties of the concerned orbital 
  Reference    Z. Naturforsch. 48a, 257—260 (1993); received December 24 1991 
  Published    1993 
  Keywords    Electronic structure, Ionisation cross-section, Compton scattering 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0257.pdf 
 Identifier    ZNA-1993-48a-0257 
 Volume    48 
3Author    C. TavardRequires cookie*
 Title    Double-Ionisation Processes and Electronic Structures  
 Abstract    The electron momentum distribution of a given target can be extracted, under impulsive condi-tions, from the simple ionisation processes relevant to Compton collisions. This document classifies and investigates the physical mechanisms of double ionisation, in connection with the target elec-tronic structure. 
  Reference    Z. Naturforsch. 48a, 251—254 (1993); received October 17 1991 
  Published    1993 
  Keywords    Double-ionisation processes, Scattering cross-section, Electron scattering, inelastic, Electronic structure 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0251.pdf 
 Identifier    ZNA-1993-48a-0251 
 Volume    48 
4Author    M. A. Coplan, J. H. Moore, J. A. TossellRequires cookie*
 Title    (e, 2 e)-Spectroscopy and the Electronic Structure of Molecules. A Short Review with Selected Examples  
 Abstract    The simple plane wave target Hartree-Fock impulse approximation for the (e, 2e) reaction is developed. One result of the approximation is the separation of the expression for the (e, 2e) cross-section into a kinematic factor and a structure factor that contains all of the information about the target. When the target is a molecule, the structure factor can be further separated into atomic terms and a geometric term. This is illustrated for a simple one-electron homonuclear diatomic molecule. Three examples of the application of (e, 2e) spectroscopy to systems of chemical interest are given. They are borazine (inorganic benzene), the methyl siloxanes and the inorganic complex trimethylamine boron trifluoride. 
  Reference    Z. Naturforsch. 48a, 358—370 (1993); received January 30 1992 
  Published    1993 
  Keywords    (e, 2e)-Spectroscopy, Electron momentum spectroscopy, Electron momentum density, Electronic structure 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0358.pdf 
 Identifier    ZNA-1993-48a-0358 
 Volume    48 
5Author    Tanja Asthalter, Wolf WeyrichRequires cookie*
 Title    The Anisotropy of the Reciprocal Form Factor and the Electronic Structure of Crystalline Lithium Hydride  
 Abstract    New high-precision measurements of the isotropic as well as of three directional Compton spectra of lithium hydride have been carried out using 24 'Am as a y-ray source. In order to account for the extreme sensitivity of LiH powder to atmospheric moisture, the final data (i.e. the reciprocal form factor) were corrected for the LiOH content determined by titrimetric analysis. For the interpreta-tion of the data, theoretical calculations were carried out using a Hartree-Fock program for periodic systems (CRYSTAL). Basis sets published by Dovesi et al. were used, one of which allows for polarisation of both the hydride and lithium ions. Comparison of the theoretical data with the experiment shows much better agreement of the results of complete solid-state calculations that take into account higher-order effects (polarisation and covalency) than those obtained by Löwdin orthogonalisation of free-ion wave functions (which assumes pure ionicity, neglecting all but first-order effects). The influence of further polarisation functions on the reciprocal form factor is inves-tigated and discussed. The remaining discrepancies are attributed to electron-electron correlation. 
  Reference    Z. Naturforsch. 48a, 303—309 (1993); received January 13 1993 
  Published    1993 
  Keywords    Compton spectroscopy, Reciprocal form factor, Ionic crystal, Electronic structure, Lithium hydride 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0303.pdf 
 Identifier    ZNA-1993-48a-0303 
 Volume    48 
6Author    B. K. SharmaRequires cookie*
 Title    Compton Scattering from Heavier Metals  
 Abstract    The use of Compton scattering in the determination of electronic structure has grown consider-ably in the last two decades. With the advent of synchrotron radiation it has become possible, even with good resolution, to measure several single-crystal orientations to determine three-dimensional electron momentum distributions. Although most of the earlier work has been directed to low-Z materials, in the last few years medium and high-Z metals have also been investigated with this technique. In this paper we present a review of these studies on heavier metals with particular attention to the difficulties encountered. Compton profile measurements from techniques based on energetic ion beams are also considered briefly. 
  Reference    Z. Naturforsch. 48a, 334—342 (1993); received December 31 1991 
  Published    1993 
  Keywords    Compton profiles, Electron momentum distributions, Electronic structure, Brems-strahlung, Ion Compton profile 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0334.pdf 
 Identifier    ZNA-1993-48a-0334 
 Volume    48