Density functional calculations were made of the potential energy surface for the binding and diffusion of a H atom on a (111) adatom structure with 2 adatom and 1 rest-atom dangling bonds per unit cell. These were used to model the (111)-(7 x 7) surface. It was found that H binding was stronger at rest-atom, than at adatom, sites by about 0.2eV; in good agreement with desorption data. This result, together with a detailed analysis of H diffusion paths and barriers, indicated that R  A  R jumps provided the mechanism for H diffusion at low coverages. The calculated barrier for such jumps agreed well with experimental data.

A.Vittadini, A.Selloni: Physical Review Letters, 1995, 75[26], 4756-9