LATTICE-GAS MODEL OF DIFFUSION OF NH3 ON RE(0001)

A lattice-gas model for the chemical diffusion of NH3 on Re(0001) is p resented. The system is modelled as a triangular lattice gas with near est-neighbour repulsive lateral interactions. The average jump rate an d the static structure factor are calculated within the cluster variat ion method framework by using a cluster of seven sites. Then the chemi cal diffusion coefficient is evaluated in the Darken approximation. Th is results in the jump rate and diffusion coefficient strongly increas ing with coverage in agreement with experimental measurements.