Diffusion of a vacancy on Fe(1 0 0): A molecular-dynamics study

The diffusion of a surface vacancy on Fe(1 0 0) has been studied at various temperatures by means of molecular-dynamics simulations in conjunction with a many body potential in the context of the embedded atom method. This interatomic potential was recently constructed by fitting its parameters to both experimental and first-principles results. From the analysis of the vacancy jumps, three main diffusion mechanisms have been investigated. The first one corresponds to the migration of the vacancy on the surface layer (intra-layer jumps) by hopping to a neighboring site, while the two others involve the participation of an atom of the second layer (inter-layer jumps) as well. The temperature dependence of the associated diffusion coefficients follows an Arrhenius behavior, from which the migration energies and pre-exponential factors were deduced. It was found that one of the mechanisms corresponding to inter-layer jumps is energetically slightly favored over the two other processes and in addition, its diffusivity is about six times higher than that of the two others. Our results show that the contribution of vacancy diffusion to mass transport is important.