  Using density-functional theory we compute the energy barriers and attempt
frequencies for surface diffusion of Ag on Ag(111) with different lattice
constants, and on an Ag adsorbate monolayer on Pt(111). We find that the
attempt frequency is of the order of 1 THz for all the systems studied. This is
in contrast to the so-called compensation effect, and to recent experimental
studies. Our analysis suggests that the applicability of simple (commonly used)
scaling laws for the determination of diffusion and growth parameters is often
not valid.
