Rolling: A fast diffusion mechanism for small clusters on a solid surface

We have performed molecular-dynamics simulations to analyze diffusion of small clusters on a solid surface, and found a new diffusion mechanism in which a spherical-like cluster can move rapidly with a rolling motion. When applied to Ni-n (n = 1 - 14) clusters on the Au(110)-(1 x 2) surface, our model predicted a cluster-size dependence in diffusion, with the most spherical-like Ni-4 and Ni-13 having the largest diffusion constants. Our model also confirmed that diffusion of Ni across the [1 (1) over bar 0] troughs is slower than diffusion along the troughs. For the transverse diffusion, rolling of Ni-4 is, once again, an effective mode of cluster motion. [S0163-1829(99)03139-2].