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  • 1
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The equilibrium lattice parameter and bandstructure of copper monolayers, both in the square (100) and hexagonal (111) symmetry, have been determined using self-consistent full-potential local density approximation (LDA) calculations. Two quite different procedures have been employed: FILMS, a linear-combination-of-gaussian-type-orbitals method, and a full-potential linearized augmented plane-wave (F-LAPW) method. The copper monolayer is bound with respect to the atomic LSDA ground state in the configurationd 10 s 1. Nearest-neighbor distancesa nn are determined as 4.25 a.u. in the square geometry and 4.42 a.u. in hexagonal geometry, the latter being favored in energy by 0.33 eV/atom. Both monolayers thus exhibit a nearest-neighbor distance substantially shorter than that found in bulk copper,a nn=4.8238 a.u. Excellent agreement between the two methods is obtained for the bandstructure, with no indication of ad-band hole at theM point (corner) of the Brillouin zone, in contrast to some other recent self-consistent calculations. Combined use of the von Barth-Hedin LDA and scalar-relativistic corrections produces the smallest gap at theM point, 0.15 eV, at the Hedin-Lundqvist equilibrium geometry. This may be suggestive evidence for the origin ofd-band holes when combined with further approximations in the representation of the one-electron orbitals and the charge density.
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  • 2
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We consider the convergence and energy-bounding properties of the Nosanow cluster expansion in combination with the pair correlation function employed by Wu and Krumhansl. We employ the transfer-integral method and one-dimensional model quantum solid developed by Trickey and Nuttall. The results of our investigation differ somewhat from those of Wu and Krumhansl. Their correlation function yields a minimum value of the cluster approximation to the cohesive energy for the model system which is significantly different from the rigorous variational result. The cluster approximation gives a substantially different best value of the pair function variation parameter than that determined by the transfer integral. The cluster-expansion convergence rates reflect these difficulties. Restriction of the variation of the single-particle functions to a parametrized Gaussian eliminates these discrepancies. Such nonphysical behavior is a priori possible with any choice of pair function.
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  • 3
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The effect of choosing a Jastrow function of the WKB formexp (−k/r5) for use in the Nosanow cluster calculation of the quantum crystal ground state is studied via a previously developed exact one-dimensional model. The computed convergence rates confirm the inability of this form to resum the cluster expansion so as to provide a meaningful variational minimum.
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  • 4
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We consider a one-dimensional linear lattice of particles whose mass, pair potential, and nearest neighbor separation are those of a real rare gas crystal. Numerical solution of the Hartree equation shows that the model behaves as a quantum crystal in the low mass, weak attraction case. In the basic Nosanow cluster approximation the cohesive energy of this helium-like system drops from 6.903°K/N (Hartree) to 3.64°K/N. When all except nearest neighbor correlations in the Jastrow function are taken as unity, the result is 3.69°K/N. For the case of nearest neighbor correlations only, we introduce a positive integral operator with properties akin to those of a transfer matrix and thus form a rigorous upper bound on the cohesive energy of the model system. The convergence rate of the Nosanow expansion is shown to depend on the ratio of the two highest eigenvalues of this operator.
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  • 5
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: The results of a simple local-density energy band model (Xα) are used to carry through a calculation of the phonon dispersion relations in fcc Ne and Ar. Adiabatic phonons, calculated from the computed Xα total energy surface, are perturbed by the Fröhlich Hamiltonian with electron-phonon matrix elements calculated from the Xα energy bands. The use of low-order perturbation theory gives results in fair comparison with observed values, but shows the general scheme to be feasible. Except for questions of the exact physical content of the Xα model itself, the calculation is entirely ab initio, and is believed to be the first such achieved in insulators.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In our previous work, the stopping properties of metallic and covalent films were investigated. Here we consider an ionically bound film. The energy loss of a proton in an LiF monolayer (LiF-1L) is calculated in orbital fashion, based on kinetic theory. The required momentum density and mean excitation energy are obtained from the local density approximation and local plasma approximation respectively. For comparison, the LiF molecule is treated by use of a large intermolecular distance in the film. We find the stopping cross section of the LiF molecule to be only slightly larger than that for the LiF-1L. The Bragg rule (additivity of stopping for the corresponding atoms) is not valid for the ionically bound molecule nor the corresponding extended system, but may be valid if additivity of stopping of atomic ions is assumed. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 8
    ISSN: 0020-7608
    Keywords: broken symmetry ; general spin orbitals ; symmetry dilemma ; spin symmetry ; symmetry in density functional theory ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Kohn-Sham (KS) procedure for variational minimization of the Hohenberg-Kohn density functional utilizes a one-particle reduced density matrix of assumed diagonal form, hence depends implicitly on a set of auxiliary states. Originally, the auxiliary state was assumed to be a single determinant with doubly occupied spin orbitals, i.e., of the same form as in “restricted” Hartree-Fock theory. The pragmatic and formal extension of the KS procedure to noninteger occupation numbers requires extension to more general forms of the auxiliary state or even its replacement by an auxiliary ensemble. Though attention has been given to the symmetry properties of the KS one-matrix, its spin and time-reversal symmetries have not been classified along the lines of Fukutome's treatment of the generalized Hartree-Fock problem. Here we show that, in the context of constrained search density functional theory (DFT), Fukutome's analysis goes through essentially unaltered. We then consider the broken symmetry consequences for the case that the KS one-matrix is restricted to a single-determinantal KS auxiliary state.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 451-460, 1998
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  • 9
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We systematize and clarify the significance and relationship of recently published numerical findings regarding atomic and molecular anions to both density functional theory fundamentals and approximations. Calculations for F− with all-numerical codes are included as brief examples. © 1997 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 42 (1992), S. 1037-1045 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Some time ago Min et al. [Phys. Rev. B 30, 5076 (1984)] found the near-equilibrium sequence of phases of paramagnetic crystalline H to be (in order of increasing energy) simple cubic (SC), hexagonal close packed (HCP), body-centered cubic (BCC), and face-centered cubic (FCC), with FCC and HCP substantially separated (about 60 mRy/atom). This result is counterintuitive on three counts when compared with crystalline Li. That comparison suggests that HCP should lie only slightly below FCC and both should be substantially below BCC. (Simple cubic should lie lowest in H but not in Li because of the difference in orbital occupancy.) We have redone the calculations with our published full-potential linearized augmented plane wave code WIEN. We find the sequence of phases with increasing energy to be SC, HCP, FCC, and BCC, the ordering expected from solid Li. By direct exploration of dense k-space meshes, we show that the difference in predictions results from a k-space mesh extrapolation technique used by Min et al.
    Additional Material: 1 Ill.
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