Size dependence of the diffusion coefficient for large adsorbed clusters

We report systematic and accurate simulation studies of the diffusion coefficient (D) of two-dimensional clusters using a lattice model. For small cluster sizes, we observe a size dependence of D that is consistent with theoretical predictions for a periphery-diffusion mechanism. For larger sizes, we find a much weaker size dependence of D. This is in agreement with that seen in recent experimental studies of homoepitaxial, metal fcc(001) cluster diffusion. The weak size dependence of D for larger clusters correlates well with the concerted motion of kinks. We propose an expression to describe this behavior.