Self-diffusion behaviors of two-dimensional compact hexagonal Cu-7 and Pt-7 clusters on (1 1 1) surface are studied with molecular dynamics simulation. The diffusion barriers (E-m) and prefactors (D-0) are determined from the Arrhenius diagram and compared with recent low-temperature field ion microscopy experiment. We find that D-0 of Pt-7 cluster is about 35 times larger than that of Cu-7 cluster. From the calculated phonon spectral densities of adatoms, we suggest that the different diffusion behaviors of the two clusters may result from strong interactions between the Pt adatoms and surface atoms, which make the nonequivalent self-diffusion processes, which can produce a high prefactor, occur more easily for Pt-7 cluster. (C) 2008 Elsevier B. V. All rights reserved.