Double rotation mechanism in small Cu clusters concerted diffusion over Cu{1 1 1} surfaces

In this work, we study the role of the double rotation mechanism in the concerted diffusion of two-dimensional small Cu clusters (up to 10 atoms) over Cu{1 1 1} surfaces. Our results show that the necessary energy to diffuse the cluster on any direction over the surface (overall activation energy) increases proportionally to the cluster size. However, the minimum energy necessary to just move the cluster center of mass presents a nonmonotonic increase. The reason for this behavior relies on the double rotation mechanism, which is observed in some clusters with diamond shape configuration. Consequently, clusters as big as hexamers can be expected to be surprisingly mobile with activation energies around 0.15 eV.