Jr. Sanchez et Jw. Evans, Diffusion of small clusters on metal (100) surfaces: Exact master-equationanalysis for lattice-gas models, PHYS REV B, 59(4), 1999, pp. 3224-3233
Exact results are presented for the surface diffusion of small two-dimensio
nal clusters, the constituent atoms of which are commensurate with a square
lattice of adsorption sites. Cluster motion is due to the hopping of atoms
along the cluster perimeter with various rates. We apply the formalism of
Titulaer and Deutch [J. Chem. Phys. 77, 472 (1982)], which describes evolut
ion in reciprocal space via a linear master equation with dimension equal t
o the number of cluster configurations. We focus on the regime of rapid hop
ping of atoms along straight close-packed edges, where certain subsets of c
onfigurations cycle rapidly between each other. Each such subset is treated
as a single quasiconfiguration, thereby reducing the dimension of the evol
ution equation, simplifying the analysis, and elucidating limiting behavior
. We also discuss the influence of concerted atom motions on the diffusion
of tetramers and larger clusters. [S0163-1829(99)05704-5].