Diffusion on a fcc (111) surface in the presence of repulsion and non-equivalent adsorption sites

Diffusion on a fcc(lll) surface will be studied theoretically. Diffusion pr oceeds through non-equivalent hcp and fee sites with different adsorption e nergy. Repulsive interaction between particles in the first neighbour sites and change of saddle point energy due to interaction are included. In this model the repulsion to the next neighbour site results in the inadequately increased diffusion coefficient. The large difference of adsorption energy between hcp and fee sites depresses diffusion at higher coverages and diff usion coefficient has maximum at Theta = 1/2. Inclusion of the change of th e saddle point energy reduces increase of D and results in a tame local min imum, emphasizing a local maximum. (C) 2000 Elsevier Science B.V. All right s reserved.