Activation free energy and entropy for the normal and exchange selfdiffusion processes on Cu(100)

A theoretical analysis is made of the free energy and entropy barriers in the exchange and bridge diffusion paths for adatom selfdiffusion on Cu(100). The effective medium theory is used to calculate the energetics. A Monte Carlo method is used to find the free energy and entropy differences between the atom located in the stable fourfold hollow site and in the transition state. The activation entropy is found to be similar for the two paths. The resulting prefactor for the diffusion process is in excellent agreement with experiment. The variation of the activation free entropy with temperature is quite different from the outcome of a harmonic model but in qualitative agreement with the results using the quasi-harmonic approximation.