Energy barriers and attempt frequencies for the surface diffusion of Ag on Ag(111), and on a Ag adsorbate monolayer on Pt(111), were calculated for various lattice constants by using density-functional theory. It was found that the attempt frequency was of the order of 1THz for each system. The analysis suggested that the applicability of simple and commonly-used scaling-laws for the determination of diffusion and growth parameters was often not valid. It was proposed that adatoms should be described by a more delocalized nuclear wave function. Long-range adatom-adatom and atom-step interactions became noticeable, and atomic diffusion then occurred more by so-called flying over several lattice constants than by hopping to nearest-neighbor sites. Cluster diffusion could also be enhanced in strained systems. The importance of these effects was difficult to assess theoretically.

Density-Functional Theory Calculations of Hopping Rates of Surface Diffusion. C.Ratsch, M.Scheffler: Physical Review B, 1998, 58[19], 13163-6