No abstract available

No abstract available

[en] In recent work, the authors have provided a rigorous physical interpretation for the exchange energy and potential (or functional derivative) as obtained within the local-density approximation via the Harbola-Sahni formulation of many-electron theory. In this article, the authors analyze the gradient-expansion approximation (GEA) for these properties from the same physical perspective. The source charge distribution in this approximation is the GEA Fermi hole to O(∇³). This charge distribution is unphysical, so that the resulting force field and work done cannot be defined in a physically meaningful manner, and the exchange energy is singular. Thus, when viewed from the perspective of a source charge, the existence of the gradient expansions for the potential and energy is questionable. The authors next discuss the conventional method of employing a screened-Coulomb interaction to eliminate the singularities due to the GEA source charge, and show that it leads to inconsistent results. These inconsistencies are also intrinsic to a proof of the inequivalence of the Harbola-Sahni and Kohn-Sham exchange potentials within the GEA. Thus, although the inequivalence of these potentials has been established by other analyses, this proof is shown not to be rigorous. Finally, the authors demonstrate that when the physics of the GEA exchange source charge is corrected by the satisfaction of sum rules, the modified charge distribution then leads to a well-behaved local exchange potential and exchange energy density, and to a finite exchange energy. The consequences of this analysis on the gradient expansions for the correlation and exchange-correlation potential and energy are also noted

[en] Surface-molecule interactions and reactions are important elementary steps of catalytic reactions. Since they involve interactions between infinite and finite systems, modelings are necessary for theoretical investigations of catalytic reactions on a surface. The cluster model (CM) is most frequently used for quantum chemical calculations but neglects the effect of the bulk solid. For including such effects, embedding the cluster onto a surface (actually into a larger cluster) is a method proposed by Grimley and Pisani, and dipping the adcluster (admolecule + cluster) onto the electron bath of the solid and letting the system be at equilibrium for electron and spin exchanges is another model proposed by Nakatsuji. The authors show some applications of the embedding cluster model (ECM) and the dipped adcluster model (DAM)

[en] Published in summary form only

[en] The results of recent experimental studies of the degree of positive ionization of clusters sputtered from a number of metal surfaces by keV-ion bombardment are analyzed in terms of an earlier proposed model. The model assumes that in addition to electron exchange, there exists another mechanism of cluster ionization - thermionic emission of electrons from clusters. The calculations qualitatively reproduce the experimental data

[en] We point out that the e² dependence of the term in the correlation energy of a high-density electron gas, proportional to the gradient squared of the charge density, was rigorously derived by Ma and Brueckner only for infinitely long-wavelength variations in the charge density. We also correct an error made in obtaining the coefficient of this term which arose because of long-range Coulomb anomalies in the exchange energy which they subtracted from the exchange-correlation energy

[en] Ortho-para conversions channel of positronium in a cool plasma with sufficiently low, kTe<<1/4xRy, electron temperature is considered

No abstract available

[en] The electron-exchange effects on the charge capture process are investigated in degenerate quantum plasmas. The Bohr-Lindhard formalism with the effective interaction potential is employed to obtain the charge capture radius, capture probability, and capture cross section as functions of the impact parameter, projectile energy, electron-exchange parameter, Fermi energy, and plasmon energy. The result shows that the electron-exchange effect enhances the charge capture radius and the charge capture cross section in semiconductor quantum plasmas. It is also found that the charge capture radius and charge capture cross section increases with an increase of the Fermi energy and, however, decreases with increasing plasmon energy. Additionally, it is found that the peak position of the charge capture cross section is receded from the collision center with an increase of the electron-exchange parameter