Role of lattice vibrations in adatom diffusion

We have examined the impact of the vibrational free energy on self-diffusion on Cu(100) and Ag(100) within the framework of transition state theory. The local thermodynamic functions are calculated from vibrational density of states extracted using interaction potentials based on the embedded atom method. We find that, as temperature rises to 600 K, vibrational contributions lead to a decrease of the preexponential factor of about 2 orders of magnitude, a lowering of the barriers by about 10%, and an increase in the activation free energy by about 20%. The net effect on the diffusion constant is significant.