A study was made of variations in the activation barriers, to the self-migration of adatoms on face-centered cubic (001) surfaces, as a function of the number of movable substrate atoms. Two mechanisms were considered. One was the hopping of an adatom from one 4-fold hollow site, to an adjacent 4-fold hollow site, via a 2-fold bridge site. The other was the exchange of the adatom with an atom in the first surface layer. Although both mechanisms distorted the lattice atoms from their ideal positions, the second process was found to lead to much greater distortions than the first. There was a more than 25% reduction in the barrier to atomic exchange as the number of substrate atoms was increased from a low to very high. This was shown to be due to a sharing of the lattice distortion over many substrate atoms, thus significantly reducing the distortion due to each atom. On the other hand, the explicit inclusion of kinetic exchange-correlation electronic energy terms in the interactions was still essential for predicting the energetically favored self-diffusion mechanism on the face-centered cubic (001) surface.

L.S.Perkins, A.E.DePristo: Surface Science, 1995, 325, 169-76