First-principles calculations were made of vacancy behavior. They were based upon the generalized-gradient approximation of density-functional theory, and used the all-electron full-potential Korringa-Kohn-Rostoker Green’s function method. This guaranteed the correct embedding of a point-defect cluster in an otherwise perfect crystal. Firstly, a predicted repulsion of the first-nearest neighbor divacancy was confirmed, and the repulsion micro-mechanism was quantified. By using calculated results for vacancy formation energies and divacancy binding energies in Na, Mg and Al, it was shown that the single vacancy in nearly free-electron systems became very stable with increasing free-electron density; due to the screening effect. The formation of a divacancy destroyed the stable electron distribution around the single vacancy; resulting in the repulsion of 2 vacancies on first-nearest neighbor sites, so that the first-nearest neighbor divacancy was unstable. Secondly, it was shown that the cluster expansion converged rapidly for the binding energies of vacancy agglomerates in Al. The binding energy of 13 vacancies, consisting of a central vacancy and 12 nearest-neighbors, was reproduced to within an error of 0.002eV per vacancy; if many-body interaction energies up to 4-body terms were taken into account in the cluster expansion. This compared with the average error, of more than 0.1eV, of the glue models which were often used to provide interatomic potentials for simulations. The same convergence, as that obtained for vacancies, was found for the cluster expansion of the binding energies of impurities. The present cluster-expansion approach for the binding energies of agglomerates of vacancies and impurities was expected to provide accurate data for constructing interaction-parameter models for simulations.

Full-Potential KKR Calculations for Vacancies in Al - Screening Effect and Many-Body Interactions. T.Hoshino, M.Asato, R.Zeller, P.H.Dederichs: Physical Review B, 2004, 70[9], 094118 (7pp)