The potential and the functional to be used in a density functional theory description of the formation and migration energies of monovacancies in Ni were considered. As the formation enthalpy was not well-known experimentally at 0K, the first step was to choose structural, magnetic and elastic properties, for the bulk, which were well-established experimentally. A comparison was made of the local spin density approximation and generalized gradient approximation exchange-correlation functionals. It was concluded that the contribution of non-local generalized gradient approximation terms to describing correctly the electronic density was necessary in order to determine the formation and migration enthalpies and activation energy of a monovacancy. The calculated formation (Hvf) and migration (Hvm) enthalpies differed significantly for the 2 approaches. The over-estimation of the local spin density approximation approximation was 0.25eV for Hvf and 0.23eV for Hvm with respect to the generalized gradient approximation. This led to a gap of 0.48eV, between the 2 methods, for the activation energy. It was shown that the generalized gradient approximation results were comparable with experimental data if the thermal expansion contribution was taken into account via lattice parameter variations. It was shown that the activation energy was nearly independent of thermal expansion effects. Thus, it was expected that the curvature of the Arrhenius plot of the diffusion factor, near to the melting point, was due mainly to the contribution of divacancies.

Density Functional Calculations of the Formation and Migration Enthalpies of Monovacancies in Ni - Comparison of Local and Non-Local Approaches. E.H.Megchiche, S.Pérusin, J.C.Barthelat, C.Mijoule: Physical Review B, 2006, 74[6], 064111 (9pp)