Adatom dynamics and diffusion in a lattice-gas model were considered, for the case of O on a W(110) surface, under conditions where adatom-interaction effects were large. A particular study was made of the behavior of the tracer and collective diffusion coefficients, as a function of temperature, upon crossing over from a high-temperature disordered phase to a low-temperature symmetry-broken phase. This was done by using a combined analytical and numerical approach which was based upon a recently developed dynamic mean field theory; in addition to conventional Monte Carlo simulations. In the present case, the cause of a strong temperature-dependence of the effective activation barrier close to an order-disorder transition (and a non-Arrhenius behavior of the diffusion coefficients) could be traced to the dependence of the average microscopic jump rate in the dynamic mean field model. This was contrary to the usual assumption that thermodynamics controlled diffusion near to phase transitions. The behavior of the average microscopic jump rate was, in turn, found to arise mainly from critical effects in the short-term behavior of the waiting-time distribution of single-particle jumps. The latter was an experimentally accessible quantity. The long-term decay of the waiting-time distribution was then used to define another effective barrier which exhibited no anomalous effects near to the transition.

Adatom Dynamics and Diffusion in a Model of O/W(110) I.Vattulainen, J.Merikoski, T.Ala-Nissila, S.C.Ying: Physical Review B, 1998, 57[3], 1896-907