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1993[X]
21Author    Jiahu Wang, VedeneH. SmithRequires cookie*
 Title    Ab initio Study of the Spin Density of Nitroxide Radicals  
 Abstract    The spin densities of the nitroxides H 2 NO, (CH 3)HNO and (CH 3) 2 NO have been studied by iterative CI methods. Calculations at different geometries with various basis sets were performed. It is found that the spin distribution is delocalized within the N-O group, and substitution of the hydrogen atoms on the nitroxyl group by methyl groups changes the spin distribution significantly. Electron correlation, as well as the basis-set quality, plays an important role for the fluctuation of spin populations in the nitroxide radicals. It has been found that the spin density map can be predicted fairly well when correlation was included at certain levels and reasonable quality basis sets were employed. The spin polarization mechanism has been studied through a core excitation method. The superiority of local-spin-density (LSD) theory over the unrestricted Hartree-Fock (UHF) method in spin property studies is discussed. 
  Reference    Z. Naturforsch. 48a, 109—116 (1993); received July 4 1992 
  Published    1993 
  Keywords    Spin density, Nitroxide radicals, Iterative CI, Spin polarization effect, LDA 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0109.pdf 
 Identifier    ZNA-1993-48a-0109 
 Volume    48 
22Author    D. Bordeaux, J. X. Boucherle, B. Delley, B. Gillon, E. Ressouehe, J. SchweizerRequires cookie*
 Title    Experimental and Theoretical Spin Densities in Two Alkyl Nitroxides  
 Abstract    The spin density in the two alkyl nitroxide compounds 4-oxo-and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (tempone and tempol) has been determined by polarised-neutron diffraction and compared to theoretical predictions obtained in both the Unrestricted Hartree-Fock and the Local Spin Density approaches. 
  Reference    Z. Naturforsch. 48a, 117—119 (1993); received February 7 1992. 
  Published    1993 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0117.pdf 
 Identifier    ZNA-1993-48a-0117 
 Volume    48 
23Author    J.-X Boucherle, E. Ressouche, J. Schweizer, B. Gillon, P. ReyRequires cookie*
 Title    Spin Densities in Copper-Nitronyl Nitroxide Complexes  
 Abstract    The spin density in two copper-nitronyl nitroxide complexes, viz. bis(hexafluoroacetylacetonato)-(2,4,4,5,5-pentamethyl-l-oxy-imidazoline 3-oxide)-copper(II) and dichloro-bis(2-phenyl-4,4,5,5-tetra-methyl-l-oxy-imidazoline 3-oxide)-copper(II), has been determined by polarised-neutron diffrac-tion. Spin populations and unpaired electron wave functions have been refined. 
  Reference    Z. Naturforsch. 48a, 120—122 (1993); received February 7 1992 
  Published    1993 
  Keywords    Nitronyl nitroxide free radicals, Copper complexes, Polarised neutron diffraction, Spin density 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0120.pdf 
 Identifier    ZNA-1993-48a-0120 
 Volume    48 
24Author    B. N. Figgis, E. S. Kucharski, M. VrtisRequires cookie*
 Title    Spin Transfer through Hydrogen Bonding in [CO(NH 3 ) S (OH 2 )| |Cr(CN) 6 | ?  
 Abstract    A polarised-neutron diffraction experiment on [Co(NH 3) 5 (H 2 0)][Cr(CN) 6 ] shows the unexpected features of spin populations on the cobalt ((0.5(2) e) and the "ammine" hydrogen (0.8(1) e in total) atoms. A local density approximation DV-Xa calculation on a unit that models the molecular geometry in the crystal returns features that are broadly in agreement with the experiment. The calculation also reproduces the major features of a charge density experiment on the complex, including the low (+1.6 e) charges on the ions, in place of the formal ±3 e. 
  Reference    Z. Naturforsch. 48a, 123—126 (1993); received October 14 1991 
  Published    1993 
  Keywords    Spin density, Hydrogen bond, Local density approximation calculation, Charge den-sity, Spin transfer 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0123.pdf 
 Identifier    ZNA-1993-48a-0123 
 Volume    48 
25Author    KennethE. Edgecombe, VedeneH. Smith, Florian Müller-PlatheRequires cookie*
 Title    Nonnuclear Maxima in the Charge Density  
 Abstract    Basis-set and electron-correlation effects on the appearance and disappearance of nonnuclear maxima in the electron density are examined in Li 2 , Na 2 , Na 4 and Na 5 . It is shown that nonnuclear attractors can be removed in all cases except Li 2 . The appearance of a pseudoatom in a lithium molecule correlates remarkably well with the size of the region, in an atomic calculation, of V 2 Q (r) for the valence shell of the atom. This and the fact that the pseudoatom is also present in the promolecule indicate that the pseudoatoms are remnants of, or in fact are portions of, atoms that are not perturbed enough in the molecule to remove an essentially atomic characteristic. 
  Reference    Z. Naturforsch. 48a, 127—133 (1993); received May 27 1992 
  Published    1993 
  Keywords    Li 2, Na 2, Topological analysis, Pseudoatoms, Charge density, Electron correlation 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0127.pdf 
 Identifier    ZNA-1993-48a-0127 
 Volume    48 
26Author    N. Sukumar, B. M. Deb, Harjinder SinghRequires cookie*
 Title    Electron Charge and Current Densities, the Geometrie Phase and Cellular Automata  
 Abstract    Some consequences of the quantum fluid dynamics formulation are discussed for excited states of atoms and molecules and for time-dependent processes. It is shown that the conservation of electronic current density j(r) allows us to manufacture a gauge potential for each excited state of an atom, molecule or atom in a molecule. This potential gives rise to a tube of magnetic flux carried around by the many-electron system. In time-dependent situations, the evolution of the electronic density distribution can be followed with simple, site-dependent cellular automaton (CA) rules. The CA consists of a lattice of sites, each with a finite set of possible values, here representing finite localized elements of electronic charge and current density (since the charge density Q no longer suffices to fully characterize a time-dependent system, it needs to be supplemented with information about the current density j). Our numerical results are presented elsewhere and further development is in progress. 
  Reference    Z. Naturforsch. 48a, 134—136 (1993); received December 31 1991 
  Published    1993 
  Keywords    Electronic phase, Current density, Anyons, QFD, Cellular automata 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0134.pdf 
 Identifier    ZNA-1993-48a-0134 
 Volume    48 
27Author    ShridharR. Gadre, Christoph Kölmel, Michael Ehrig, Reinhart AhlrichsRequires cookie*
 Title    Visualization of Shapes of Molecular Anions  
 Abstract    A recently formulated strict definition of the boundary surface of molecular anions has been employed for the visualization of some simple systems. The examples included are CN", N 3 , N0 3 , ClO^, C10 3 , and Br0 3 ions. A discussion on the anisotropy of electrostatic interaction of these anions is also presented. 
  Reference    Z. Naturforsch. 48a, 137—140 (1993); received January 3 1992 
  Published    1993 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0137.pdf 
 Identifier    ZNA-1993-48a-0137 
 Volume    48 
28Author    P. Lazzeretti, M. Malagoli, R. ZanasiRequires cookie*
 Title    Use of Symmetry in Coupled Hartree-Fock Calculations of Non-linear Response Tensors in Molecules  
 Abstract    A new computational scheme for electric dipole hyperpolarizabilities has been devised within the coupled Hartree-Fock method. Only the projection of second-order perturbed orbitals onto the subspace spanned by unperturbed virtual orbitals is computed. The entire molecular symmetry is exploited to reduce computational effort: a reduced two-electron integral file containing only sym-metry-distinct matrix elements over the atomic basis functions is processed at each iteration. In addition, only symmetry-independent first-and second-order perturbed density matrices need to be calculated. An efficient computer program implementing the present approach has been developed. 
  Reference    Z. Naturforsch. 48a, 141—144 (1993); received September 23 1991 
  Published    1993 
  Keywords    Second hyperpolarizability, Ab initio calculation, Molecular symmetry 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0141.pdf 
 Identifier    ZNA-1993-48a-0141 
 Volume    48 
29Author    SudhirA. Kulkarni, ShridharR. GadreRequires cookie*
 Title    On the Topography of Electron Momentum Densities of Linear Molecules  
 Abstract    A topographical study of the electron momentum density (EMD) of some linear molecules is presented with special emphasis on the bond-directionality principle. A new approach to the bond-directionality (BD) principle has been proposed. This is based on the analysis of curvatures of critical points at p = 0 and elsewhere on the bonding axis. The linear molecules are classified into three broad categories: those which fully obey or disobey the BD principle as well as those which satisfy it only partly. The Laplacian of the EMD at p = 0 has been associated with the quality of the wavefunction via the electron density in the tail region. Also, the similarity in the critical structure of both the EMD and the spherically averaged EMD at the origin is brought out. 
  Reference    Z. Naturforsch. 48a, 145—150 (1993); received January 3 1992 
  Published    1993 
  Keywords    Electron momentum densities, Eigenvalues, Critical points, Topography, Bond direc-tionality 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0145.pdf 
 Identifier    ZNA-1993-48a-0145 
 Volume    48 
30Author    Jean-Louis CalaisRequires cookie*
 Title    Momentum Distribution and Charge Density in Solid-State Theory  
 Abstract    We present a discussion of a number of conceptual and methodological aspects associated with the theoretical characterization and computation of charge densities and momentum distributions in solids. The main ambition has been to stress properties that both exact and approximate quantities must possess. We have also attempted to point out conceptual and computational trends which would seem to be of importance for the future of the subject. 
  Reference    Z. Naturforsch. 48a, 151—158 (1993); received May 14 1992 
  Published    1993 
  Keywords    Solid-state theory, Charge density, Momentum density, Density matrices, Hartree-Fock approximation, Density functional theory 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0151.pdf 
 Identifier    ZNA-1993-48a-0151 
 Volume    48 
31Author    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 
32Author    A. BansilRequires cookie*
 Title    Modern Band Theory of Disordered Alloys: Basic Concepts Including a Discussion of Momentum Densities  
 Abstract    An overview of some of the basic concepts in the modern first-principles band theory of disordered alloys is given. The question of how the notion of Bloch energy bands and Fermi surfaces generalizes to the case of the disordered system, insofar as the average electronic spectrum is concerned, is stressed. The theory is illustrated with examples chosen from the work on binary alloys; a few examples of the very recent studies of disordered phases of the high-T c superconductors are also included. The application of the alloy theory to obtain electron and electron-positron momentum densities involved in the analysis of Compton scattering and positron annihilation (angular correla-tion) experiments in alloys is discussed, with a selection of relevant theoretical and experimental studies. 
  Reference    Z. Naturforsch. 48a, 165—179 (1993); received January 25 1992 
  Published    1993 
  Keywords    Disordered alloys, KKR-CPA, Momentum densities, Compton scattering, Positron annihilation (ACAR) 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0165.pdf 
 Identifier    ZNA-1993-48a-0165 
 Volume    48 
33Author    B. Hess, H. L. Lin, J. E. Niu, W.H E SchwarzRequires cookie*
 Title    Electron Density Distributions and Atomic Charges  
 Abstract    Accurate electron densities and X-ray form factors of Li, Be, F and their ions have been calculated. Electron correlation, crystal fields and ionic charge transfer change the form factors by up to a few percent, mainly in the range of sin 0/k < | Ä" 1 . Although electron correlation and crystal fields are small perturbations, their effects on the density and form factor are not additive. Densities or form factors of atomic and ionic systems are very similar; [Li°F°] and [Li + F~] procrystals differ by an effective charge transfer of not more than 0.4 e. Charge transfer and charge overlap in crystals cannot be distinguished uniquely. When the experimental data on Li 2 BeF 4 (approximately reproduced by 3/4 atomic plus 1/4 ionic procrystal) are interpreted from the atomic viewpoint, the atomic partial charges are as low as 0.1 e (Li 2 01 Be + 0,2 F4 *); when interpreted from the ionic viewpoint, the charges are much higher, namely 0.7 e. Intermediate viewpoints are also possible. 
  Reference    Z. Naturforsch. 48a, 180—192 (1993); received January 11 1992 
  Published    1993 
  Keywords    Electron densities, Form factors, X-ray diffraction, Ionic charges, Ionic bonding 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0180.pdf 
 Identifier    ZNA-1993-48a-0180 
 Volume    48 
34Author    Teiji Kobayasi, Hisashi NaraRequires cookie*
 Title    Core-Orthogonalization Effect in Pseudopotential Theory of the Charge Density Distribution of Valence Electrons in Semiconductors with Comments on the Effects in Momentum Space  
 Abstract    A pseudopotential calculation has been performed for the charge density distribution in Si and Ge, with the core-orthogonalization terms fully included. The state of a positron subject to the Coulomb field of the resultant electron distribution in Si is also calculated. A possible improvement of the calculated distributions of electrons and positrons in momentum space is discussed. 
  Reference    Z. Naturforsch. 48a, 193—197 (1993); received January 3 1992 
  Published    1993 
  Keywords    Charge density, Momentum density, Pseudopotential theory, Core orthogonalization, Semiconductors 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0193.pdf 
 Identifier    ZNA-1993-48a-0193 
 Volume    48 
35Author    Claudia Blaas, Josef Redinger, Raimund Podloucky, Peter Jonas, Peter SchattschneiderRequires cookie*
 Title    Calculation of Compton Profiles Using a Multipole Expansion of the Momentum Density  
 Abstract    A practical method for the calculation of Compton profiles for cubic systems with O and O h symmetry is presented that is based on a multipole expansion of the electron momentum density (EMD) in terms of cubic harmonics. The central quantities, the expansion coefficients, are deter-mined by a Gaussian-type integration (special directions) over the angular coordinates. From these coefficients the coefficients of an analogous expansion of the Compton profile can be directly calculated, establishing a transparent relationship between the electron momentum density and the Compton profile. This direct relationship offers the possibility of tracing back Compton-profile anisotropics to EMD anisotropics more easily, as demonstrated for MgO and FeAl. 
  Reference    Z. Naturforsch. 48a, 198—202 (1993); received December 24 1991 
  Published    1993 
  Keywords    Compton profile, Electron momentum density, Multipole expansion, MgO, FeAl 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0198.pdf 
 Identifier    ZNA-1993-48a-0198 
 Volume    48 
36Author    JohnE. HarrimanRequires cookie*
 Title    Electron Densities, Momentum Densities, and Density Matrices  
 Abstract    Relationships among electron coordinate-space and momentum densities and the one-electron charge density matrix or Wigner function are examined. A knowledge of either or both densities places constraints on possible density matrices. Questions are approached in the context of a finite-basis-set model problem in which density matrices are elements in a Euclidean vector space of Hermitian operators or matrices, and densities are elements of other vector spaces. The maps (called "collapse") of the operator space to the density spaces define a decomposition of the operator space into orthogonal subspaces. The component of a density matrix in a given subspace is deter-mined by one density, both densities, or neither. Linear dependencies among products of basis functions play a fundamental role. Algorithms are discussed for finding the subspaces and construct-ing an orthonormal set of functions spanning the same space as a linearly dependent set. Examples are presented and additional investigations suggested. 
  Reference    Z. Naturforsch. 48a, 203—210 (1993); received October 8 1991 
  Published    1993 
  Keywords    Electron density, Momentum density, Density matrix 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0203.pdf 
 Identifier    ZNA-1993-48a-0203 
 Volume    48 
37Author    Hartmut Schmider, VedeneH. Smith, Wolf WeyrichRequires cookie*
 Title    On the Inference of the One-Particle Density Matrix from Position and Momentum-Space Form Factors  
 Abstract    A modification of a recently developed method for the least-squares reconstruction of a one-par-ticle reduced density matrix from experimentally accessible expectation values is applied to the test systems of atomic beryllium and neon. The improvement of the resulting matrices through inclusion of electron correlation is demonstrated. Their quality is judged by comparison of the moments of the position and momentum densities and of the spherically averaged density matrix in a suitable representation. 
  Reference    Z. Naturforsch. 48a, 211—220 (1993); received June 3 1992 
  Published    1993 
  Keywords    Density matrix, Reconstruction, Least-squares fit, Beryllium, Neon 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0211.pdf 
 Identifier    ZNA-1993-48a-0211 
 Volume    48 
38Author    VedeneH. Schmider, Smith, Wolf WeyrichRequires cookie*
 Title    Hartmut  
 Abstract    A recently developed method for the least-squares reconstruction of one-particle reduced density matrices from one-particle expectation values has been applied to isotropic Compton profiles of neon from the literature. The resulting densities in momentum and position space are compared with the ones obtained from ab-initio calculations. 
  Reference    Z. Naturforsch. 48a, 221—226 (1993); received June 3 1992 
  Published    1993 
  Keywords    Density matrix, Compton profile, Least-squares fit, Atomic orbitals, Reconstruction 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0221.pdf 
 Identifier    ZNA-1993-48a-0221 
 Volume    48 
39Author    A. Kaprolat, W. SchülkeRequires cookie*
 Title    Nondiagonal Response of Electrons by Coherent Inelastic X-Ray Scattering  
 Abstract    The experimental knowledge of the dielectric response of electrons within a solid is up to now mainly gained by inelastic scattering experiments, using a plane wave as initial state of the probe particle. These experiments allow the measurement of the dynamical structure factor, related to diagonal elements of the inverse dielectric matrix e~ \ We present a new type of scattering experiment that uses as initial state of the probe a standing wave field, thus allowing the experimental determi-nation of non-diagonal elements of £ _1 . Comparison of the experimental results with a plasmon-band model leads to direct experimental evidence for plasmon-banding in Si. 
  Reference    Z. Naturforsch. 48a, 227—232 (1993); received January 3 1992 
  Published    1993 
  Keywords    Inelastic scattering of X-rays, Dielectric response, Dielectric matrix, Local field effect, Plasmon-band model 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0227.pdf 
 Identifier    ZNA-1993-48a-0227 
 Volume    48 
40Author    K. SturmRequires cookie*
 Title    Dynamic Structure Factor: An Introduction  
 Abstract    The doubly differential cross-section for weak inelastic scattering of waves or particles by many-body systems is derived in Born approximation and expressed in terms of the dynamic structure factor according to van Hove. The application of this very general scheme to scattering of neutrons, x-rays and high-energy electrons is discussed briefly. The dynamic structure factor, which is the space and time Fourier transform of the density-density correlation function, is a property of the many-body system independent of the external probe and carries information on the excitation spectrum of the system. The relation of the electronic structure factor to the density-density response function defined in linear-response theory is shown using the fluctuation-dissipation theorem. This is important for calculations, since the response function can be calculated approximately from the independent-par-ticle response function in self-consistent field approximations, such as the random-phase approxima-tion or the local-density approximation of the density functional theory. Since the density-density response function also determines the dielectric function, the dynamic structure can be expressed by the dielectric function. 
  Reference    Z. Naturforsch. 48a, 233—242 (1993); received December 10 1991 
  Published    1993 
  Keywords    Scattering theory, Dynamic structure factor, Inelastic photon scattering, Inelastic elec-tron scattering, Inelastic neutron scattering, Dielectric function 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0233.pdf 
 Identifier    ZNA-1993-48a-0233 
 Volume    48 
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