Susan Rachel Atlas

First-principles calculation of the Mg(0001) surface relaxation

Abstract First-principles calculations for the clean Mg(0001) surface indicate that the first three interlayer spacings are expanded with respect to the bulk value by 1.5%, 0.5%, and 0.1%, respectively. These results are in excellent agreement with an analysis of low-energy electron diffraction I–V spectra that yields changes in the first three interlayer spacings of 1.9%, 0.8%, and −0.4%, respectively [P.T. Sprunger, K. Pohl, H.L. Davis and E.W. Plummer, submitted]. The calculations also show that the outward relaxation is accompanied by a 2.8% decrease in the p σ population of the surface-layer atoms (pσ is defined with respect to the surface normal). This is somewhat smaller than the 7.8% decrease reported to accompany the outward relaxation of the clean Be(0001) surface [P.J. Feibelman, Phys. Rev. B 46 (1992) 2532].

Energy dependence on fractional charge for strongly interacting subsystems.

The energies of a pair of strongly interacting subsystems with arbitrary noninteger charges are examined from closed- and open-system perspectives. An ensemble representation of the charge dependence is derived, valid at all interaction strengths. Transforming from resonance-state ionicity to ensemble charge dependence imposes physical constraints on the occupation numbers in the strong-interaction limit. For open systems, the chemical potential is evaluated using microscopic and thermodynamic models, leading to a novel correlation between ground-state charge and an electronic temperature.