Vibrational free energy contribution to self-diffusion on Ni(100), Cu(100) and Ag(100)

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The role of lattice vibrations in self diffusion on the (100) surfaces of Ag, Cu and Ni is investigated within the framework of transition state theory. Local vibrational density of states are calculated in the harmonic and quasi-harmonic approximation from which the vibrational activation internal energy and entropy are derived. For the present study, we use two sets of interaction potentials from the embedded atom method. We show that entropy contributions lower the pre-exponential factor by up to two orders of magnitude and vibrational internal energy decreases the static-lattice barrier at 600 K by up to 10% for Cu and Ag and 8% for Ni. We also discuss the effect of thermal expansion on the activation barrier.