Surface self-diffusion of Re adatom on the Re cluster with hexahedral structure

The surface self-diffusion of a single adatom on the rhenium cluster with hexahedral structure is studied by molecular dynamics simulations. The minimum energy paths and the corresponding energy barriers are determined by the nudged elastic band method. The two diffusion mechanisms, i.e., direct hopping and exchange, for adatom across the step edge are investigated. For the adatom migration from a (0 0 0 1) facet to a neighboring (1 1¯ 0 1) facet, there are two paths, and the corresponding Ehrlich-Schwoebel barriers are so dramatic high that the diffusion crossing the step edge could not take place below 101 K. Three diffusion paths for the adatom across the step edge between two neighboring (1 1¯ 0 1) facets have been discussed. We find that the Ehrlich-Schwoebel barriers of these paths are high and the diffusions on (1 1¯ 0 1) facet are difficult to take place below 261 K. The calculated energy barrier for adatom diffusing along the step edge is lower than that for adatom on the (0 0 0 1) facet. The results show that the adatom on the (0 0 0 1) facet should be trapped by the step edge, and then diffuses along the step edge.