Classically exact overlayer dynamics: Diffusion of rhodium clusters on Rh(100)

A new method is presented for describing the classical dynamics (e. g. , diffusion, desorption) of adsorbed overlayers of atoms or molecules, starting from arbitrary interatomic potentials. Provided that a certain dynamical criterion is met, the method yields classically exact results, but with many orders of magnitude less computation than direct molecular dynamics. The approach provides, for what we believe to be the first time, a connection between stochastic lattice-gas dynamical methods and the interatomic potential function. As a sample application, the diffusion constants are computed for two-dimensional rhodium clusters of up to 75 atoms on the Rh (100) surface at T=2000 K. For clusters larger than n=15 atoms, the diffusion constant scales as n^-1. 760. 06, and the dominant mechanism for the diffusion is found to be atoms running along the edges of the cluster blocks.