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1Author    Christian Kollmar, SighartF. Fischer, MichaelC. BöhmRequires cookie*
 Title    MO-Theoretical Studies on a Model Complex for Deoxymyoglobin  
 Abstract    The origin of the displacement of the Fe atom in deoxymyoglobin with respect to the porphyrin plane in the high-spin state is examined by a qualitative molecular orbital (MO) analysis on the extended Hückel level. We find that attachment of a fifth ligand (imidazole in our model complex) to Fe(II)porphyrin favors the out-of-plane shift due to a strengthening of the bonding interaction between Fe and the nitrogen of the imidazole ligand. This results in a high-spin (5 = 2) ground state with Fe shifted out-of-plane for the five-coordinate complex instead of an intermediate spin ground state (5=1) with Fe lying in the plane for four-coordinate Fe(II)porphyrin. The relative energies of the different spin states as a function of the distance between Fe and the porphyrin plane are evaluated using an ROHF (restricted open shell Hartree-Fock) version of an INDO (intermediate neglect of differential overlap) method. We observe a level crossing between high-spin and intermediate spin states whereas the low-spin (5 = 0) state remains always higher in energy. 
  Reference    Z. Naturforsch. 53a, 755—765 (1998); received July 1 1998 
  Published    1998 
  Keywords    Metalloporphyrines, Electronic Structure, Structural Preferences, Molecular Orbital Model 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0755.pdf 
 Identifier    ZNA-1998-53a-0755 
 Volume    53 
2Author    Andrea Gruß, MichaelC. Böhm, Joachim Schulte, Klaus-Peter DinseRequires cookie*
 Title    An ab initio Hartree-Fock Investigation of Endohedral Sc@C  
 Abstract    The electronic structure of endohedral Sc@C 82 with a C 82 cage of C 2v symmetry has been studied by ab initio Hartree-Fock (HF) calculations. The optimized position of Sc in the configuration of minimum energy is predicted to be on the two-fold axis of the fullerene cage. In the corresponding configuration Sc is above the center of a hexagon of site symmetry C 2 . This structure of C 2v symmetry is nearly degenerate with C s and C t structures with Sc slightly displaced from the center of the coordinated hexagon. The binding energy of the endohedral complex is larger than 3.55 eV. The ab initio HF data of the C 2v topoisomer of the fullerene unit are compared with new experimental findings and HF results derived for the 3(C 2) topoisomer of the C 82 cage. 
  Reference    Z. Naturforsch. 53a, 801—805 (1998); received June 12 1998 
  Published    1998 
  Keywords    Endohedral Fullerenes, Electronic Structure, ab initio Calculations 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0801.pdf 
 Identifier    ZNA-1998-53a-0801 
 Volume    53 
3Author    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 
4Author    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 
5Author    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 
6Author    StadeS. Nunes, S. Sulaiman, N. Sahoo, T. P. Das, M. Frank, W. Kreische, K. B. NielsenRequires cookie*
 Title    Study of the Location of Implanted Fluorine Atoms in Silicon and Germanium through Their Nuclear Quadrupole Interactions  
 Abstract    Time Differential Perturbed Angular Distribution (TDPAD) measurements of the nuclear quadrupole hyperfine parameters for 19 F* implanted into amorphous, polycrystalline and crys-talline silicon and germanium are reported and reviewed. Two signals are observed in the crystalline materials (« 35 and 23 MHz in silicon, % 33 and 27 MHz in germanium) while only one is detected in the amorphous and polycrystalline samples (ä22 MHz in silicon, «27 in germanium). Impurity sites in these materials were modeled using a Hartree-Fock cluster procedure. The Intrabond, Antibond, and Substitutional sites in the bulk were studied in both silicon and germanium. The ATOP and Intrabond Surface sites were also studied in silicon and the results extended to germa-nium. Lattice relaxation effects were incorporated by employing a geometry optimization method to obtain minimum energy configurations for the clusters modelling each site. The electronic wave functions were obtained for each optimized cluster by applying Unresctricted Hartree-Fock theory, and these wave functions were used to calculate the nuclear quadrupole hyperfine parameters at the site of the fluorine nucleus. Comparison of the theoretical hyperfine parameters to the experimental values indicates that 19 F* located in the Intrabond and Intrabond surface sites could readily explain the higher frequency signal that has been observed. 19 F* in the Antibond and the surface ATOP sites yield hyperfine parameters consistent with the low frequency signal observed in the crystalline materials and the single signal observed in the amorphous (or polycrystalline) materials. Examina-tion of these two sites, in view of other available experimental evidence including the temperature dependence of the TDPAD signals, leads to the conclusion that the lower frequency signal is due to 19 F* implants which have come to rest at the site of dangling bonds in the bulk. These dangling bonds are created as a result of damage generated in the individual collision cascades during the implantation process. 
  Reference    Z. Naturforsch. 51a, 560—564 (1996); received December 12 1995 
  Published    1996 
  Keywords    Semiconductors, Impurities, Electronic structure, Hartree-Fock, Electric field gradient 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0560.pdf 
 Identifier    ZNA-1996-51a-0560 
 Volume    51 
7Author    35, J. N. Latosińska, J. KasprzakRequires cookie*
 Title    Solid State Effects in 4,6-Dichloropyrimidine Studied by Cl-NQR Spectroscopy and ab initio Calculations  
 Abstract    Quantum chemistry methods -ab initio -have been used for the assignment of the 35 C1-NQR resonance frequencies to particular chlorine atoms substituted in positions 4 and 6 of pyrimidine. The so-called solid state effect, that is the influence of intermolecular interactions, in particular hydrogen bond formation, on the NQR parameters has also been studied. 
  Reference    Z. Naturforsch. 55a, 343—347 (2000); received August 28 1999 
  Published    2000 
  Keywords    35 C1-NQR, 4,6-Dichloropyrimidine, Electronic Structure, B3LYP/6-31G* 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0343.pdf 
 Identifier    ZNA-2000-55a-0343 
 Volume    55 
8Author    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 
9Author    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 
10Author    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 
11Author    H. M. Petrilli, M. Marszalek, H. SaitovitchRequires cookie*
 Title    Study of the EFG Trends in Zr 2 T (T = Fe, Co, Ni) Intermetallic Compounds  
 Abstract    We use the linear muffin-tin orbital formalism, in the atomic sphere approximation, to investigate the trends of the electric field gradient (EFG) at the nucleus for the non-equivalent sites in Zr 2 T (T = Fe, Co and Ni) intermetallic compounds. As all those compounds crystallize in the same C16 crystallographic structure, they offer a rare opportunity to investigate electronic structure effects coming from transition metals on the EFG at Zr site. Those results are compared with EFG values obtained from quadrupole coupling constant measurements performed with the time differential perturbed angular correlation (TDPAC) technique, using the 181 Ta probe. 
  Reference    Z. Naturforsch. 51a, 537—543 (1996); received February 13 1996 
  Published    1996 
  Keywords    Electric Field Gradient, Intermetallic Compounds, LMTO-ASA, Electronic Structure, Nuclear Quadrupole Interactions 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0537.pdf 
 Identifier    ZNA-1996-51a-0537 
 Volume    51