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AbstractAbstract

[en] The hole-pairing problem at the dilute limit on low-dimensional bipartite and non-bipartite lattices is studied by means of the generalized Hubbard model, in which on-site (U), nearest-neighbor (V), and assited-hopping (Δt) terms are considered. The problem is [dressed by mapping the original many-body problem onto a tight-binding one in a higher-dimensional space. It is found that there is a small region around Δt/t

_{0}= 0.5, where the pairing of holes is enhanced and non-pairing of electrons exists. Pairing phase diagrams are analyzed for linear, square and triangular lattices, in comparison with those results obtained from the extended Hubbard model. (orig.)Primary Subject

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International conference on magnetism (ICM) and symposium on strongly correlated electron systems; Cairns (Australia); 27 Jul - 1 Aug 1997; 6 refs.

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Journal of Magnetism and Magnetic Materials; ISSN 0304-8853; ; CODEN JMMMDC; v. 177-181(pt.2); p. 1482-1483

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AbstractAbstract

[en] Let E(B,Z,N) denote the ground state energy of an atom with N electrons and nuclear charge Z in a homogeneous magnetic field B. We study the asymptotics of E(B,Z,N) as B→∞ with N and Z fixed but arbitrary. It is shown that the leading term has the form (ln B)

^{2}e(Z,N), where e(Z,N) is the ground state energy of a system of N bosons with delta interactions in one dimension. This extends and refines previously known results for N=1 on the one hand, and N,Z→∞ with B/Z^{3}→∞ on the other hand. (orig.)Primary Subject

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15 refs.

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AbstractAbstract

[en] The constrained minimization independent-fermion kinetic-energy kernel, δ

^{2}T_{s}[ρ]/δρ(r)δρ(r^{'}), has a zero mode for all ρ(r), while it is non-negative for ρ(r) noninteracting v representable. copyright 1996 The American Physical SocietyPrimary Subject

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AbstractAbstract

[en] The notion of the quantum defect is important in atomic and molecular spectroscopy and also in unifying spectroscopy with collision theory. In the latter context, the quantum defect may be viewed as an ancestor of the phase shift. However, the origin of the term open-quotes quantum defectclose quotes does not seem to be explained in standard textbooks. It occurred in a 1921 paper by Schroedinger, preceding quantum mechanics, yet giving the correct meaning as an index of the short-range interactions with the core of an atom. We present the early history of the quantum-defect idea, and sketch its recent developments. copyright 1997 American Association of Physics Teachers

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1.65; 30

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AbstractAbstract

[en] An analytic expression is presented for the elementary excitation spectrum of the Bose-Einstein condensate of a trapped boson system in the weakly interacting, low-density limit. Explicit analytic formulas for the elementary excitation spectrum are obtained for harmonic-oscillator traps. These formulas provide information about the behavior of the elementary excitation levels as a function of the number of atoms and their interaction strength for a given trap geometry. They also provide a low-density benchmark for results of fully numerical calculations. copyright 1997 The American Physical Society

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Konarski, J.; Mickiewicz, A.

Second international congress on theoretical chemical physics - ICTCP II

Second international congress on theoretical chemical physics - ICTCP II

AbstractAbstract

[en] Stability of motions for different potential functions describing vibrational motions of rotating molecule will be discussed. It will be shown that equilibrium position for nonrotating r

_{o}r_{j}molecule for almost all the examined potentials is a node, but for molecule described by the soft body model a critical value of rotation quantum number J_{c}occurs above which r_{o}is a saddle point, and the stable motion may occur only around r_{j}. Consequences of these results will be presented during my talkPrimary Subject

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Anon; 90 p; 1996; p. 1, Paper TuS1 9; Louisiana State University; Baton Rouge, LA (United States); 2. international congress on theoretical chemical physics; New Orleans, LA (United States); 9-13 Mar 1996

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AbstractAbstract

[en] The potential barriers for the internal rotation of silole dimers are studied theoretically using the ab initio molecular orbital method at the RHF/6-31G** level of calculations. In 2,2'-bisilole, it is found that the anti-conformation is the most stable structure in the ground state and that the potential barrier height for rotation over the perpendicular conformation is 3.3 kcal/mol. 21 refs., 4 figs., 2 tabs

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AbstractAbstract

[en] (1) The optimized effective potential method is a variant of the traditional Kohn-Sham scheme. In this variant, the exchange-correlation energy E

_{xc}is an explicit functional of single-particle orbitals. The exchange-correlation potential, given as usual by the functional derivative v_{xc}= δE_{xc}/δρ, then satisfies as integral equation involving the single-particle orbitals. This integral equation in solved semi-analytically using a scheme recently proposed by Krieger, Li and Iafrate. If the exact (Fock) exchange-energy functional is employed together with the Colle-Salvetti orbital functional for the correlation energy, the mean absolute deviation of the resulting ground-state energies from the exact nonrelativistic values is CT mH for the first-row atoms, as compared to 4.5 mH in a state-of-the-art CI calculation. The proposed scheme is thus significantly more accurate than the conventional Kohn-Sham method while the numerical effort involved is about the same as for an ordinary Hanree-Fock calculation. (2) A time-dependent generalization of the optimized-potential method is presented and applied to the linear-response regime. Since time-dependent density functional theory leads to a formally exact representation of the frequency-dependent linear density response and since the latter, as a function of frequency, has poles at the excitation energies of the fully interacting system, the formalism is suitable for the calculation of excitation energies. A simple additive correction to the Kohn-Sham single-particle excitation energies will be deduced and first results for atomic and molecular singlet and triplet excitation energies will be presented. (3) Beyond the regime of linear response, the time-dependent optimized-potential method is employed to describe atoms in strong emtosecond laser pulses. Ionization yields and harmonic spectra will be presented and compared with experimental dataPrimary Subject

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Anon; 90 p; 1996; p. 1, Paper TuI 2; Louisiana State University; Baton Rouge, LA (United States); 2. international congress on theoretical chemical physics; New Orleans, LA (United States); 9-13 Mar 1996

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AbstractAbstract

[en] We study long-range diagonal adiabatic corrections to the interaction potentials of the ground state of homonuclear alkali-metal dimers. We show that in the long-range limit the diagonal adiabatic matrix elements may be expressed as a series of inverse powers of the internuclear distance. Each of the nonzero coefficients of this expansion is a mass-dependent correction term to the dispersion coefficients. They are computed by using a complex integral representation, that transforms the molecular problem into an atomic one. Numerical results are presented. copyright 1998 The American Physical Society

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[en] The dynamics of near-threshold photoionization is a complex phenomenon in which the many-electron character of the wavefunctions plays an important role. According to generalized time-independent resonant scattering theory, the transition matrix element from an initial state to a final state is the summation of the amplitudes of direct photoionization and an indirect term in which intermediate states are involved and the resonant behavior is embedded. Studies of the interference effects of intermediate states have been explored in the cases where the direct term is negligible. In the present work, electron time-of-flight spectra of the Ar 2p satellites were measured at two angles (magic and 0 degrees) in the dipole plane with the exciting photon energy tuned in the vicinity of the Ar 2s threshold. For excitation far below or above the 2s threshold, the 2p satellites spectrum is dominated by 3p to np shakeup contributions upon the ionization of a 2p electron

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Lawrence Berkeley Lab., CA (United States); 622 p; Apr 1997; p. 188-189; ALSO AVAILABLE FROM OSTI AS DE97007345; NTIS; INIS; US GOVT. PRINTING OFFICE DEP. (UNITED STATES)

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