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A study of the variation in the calculated quantities for adatom diffusion with respect to the size of the model crystal is presented. The reported quantities include surface diffusion barrier heights, pre-exponential factors, and dynamical correction factors. Embedded atom method (EAM) potentials were used throughout this effort. Both the layer size and the depth of the crystal were found to influence the values of the Arrhenius factors significantly. In particular, exchange type mechanisms required a significantly larger model than standard hopping mechanisms to determine adatom diffusion barriers of equivalent accuracy. The dynamical events that govern the corrections to transition state theory (TST) did not appear to be as sensitive to crystal depth. Suitable criteria for the convergence of the diffusion parameters with regard to the rate properties are illustrated.

A long range adatom diffusion mechanism has been observed in simulations on the fcc (100) surfaces of embedded atom method (EAM) modeled materials. This mechanism primarily involves the adatom and two atoms in the top substrate layer. After passing through the saddle configuration the adatom is found two rows down and one row over from its original position. The movement of the adatom is like that of a knight on a chess board. The activation barrier of this mechanism is high, and it begins to appear at temperatures about half the melting temperature of the material. Due to the long range nature of this mechanism it could significantly affect the adatom diffusion rate as compared to typical hopping between adjacent minima or diffusion via the exchange mechanism.