An  ab initio  pseudopotential study was made of mono-vacancy properties in body-centered cubic material. The formation and migration enthalpies were calculated for relaxed configurations by using super-cells which contained up to 54 atomic sites. The electronic contribution to the formation entropy, which was usually neglected in such calculations, was shown to be positive and equal to 1.74k at the melting point. This large value was related to peaks in the electronic density of states, just below the Fermi level, which were due to states that were localized around the vacancy. The calculated values of the migration and formation enthalpies were found to be in excellent agreement with data obtained at low temperatures. An appreciable quadratic temperature dependence, due to electronic excitations, was shown to explain some of the experimentally observed temperature dependence of the migration enthalpy and self-diffusion activation energy. The tracer self-diffusion coefficient was calculated within the rate theory. The Arrhenius slope was found to be in excellent agreement with experimental data, as were the absolute values; provided that the electronic entropies were taken into account.

Vacancy Self-Diffusion Parameters in Tungsten: Finite Electron-Temperature LDA Calculations A.Satta, F.Willaime, S.De Gironcoli: Physical Review B, 1998, 57[18], 11184-92