By using molecular dynamics simulations, and the embedded-atom method, a study was made of the self-diffusion of single adatoms on flat, (100) and (111), surfaces. The results for the (111) surface indicated that, when the thermal energies of the atoms became larger than the energy barriers, the diffusion could no longer be represented by a simple random walk; since correlations between successive jumps became important. A simple model was presented which took account of these correlated jumps and closely reproduced the molecular dynamics data. It was also demonstrated that a knowledge of the energy barriers was insufficient for the determination of the preferred diffusion mechanism for the (100) surface, because the pre-exponential factors for the various mechanisms could differ significantly from the value which was usually assumed. A simple transition-state theory was applied, and it was found that the static barrier was equivalent to the dynamic activation energy. The pre-exponential factor was also well described, provided that the relaxation of the substrate remained small.

G.Boisvert, L.J.Lewis: Physical Review B, 1996, 54[4], 2880-9