Atomistic Investigation of Anomalous Diffusion on Surfaces: A Deterministic Approach

The observation of anomalous diffusion rates on surfaces by recent experiments has renewed interest in diffusion mechanics. In order to provide a better understanding of the atomistic motions resulting in anomalous diffusion, we have investigated the diffusion dynamics of sodium on a copper surface using conservative molecular dynamics. The properties of diffusing adatoms transitioning between normal diffusive motion and anomalous motion have then been examined. Utilizing short time approximation Lyapunov exponents, stable cantori within chaotic manifolds are identified. At the periphery of these stable cantori from which anomalous diffusion originates, we have examined the transition properties of diffusive motions with abnormally long jump properties. We have verified statistically their Levy distributions, and have examined the transition life cycle of these Levy flights using Poincare section analysis.