CPM Seminar

The Arrhenius form is well known and commonly used to describe various rate processes such as chemical reactions and diffusion. Its simplicity is intriguing but also somewhat deceptive, since the parameters extracted from an Arrhenius analysis are effective ones, thus not revealing the true microscopic nature of the process. In this talk, I focus on this problem in the context of surface diffusion within the lattice-gas model. Within this approach, there is a formally exact way of describing the surface diffusion coefficients as a product of various factors such as the average transition rate and a term arising from memory effects, which allows a direct study of where the effective surface diffusion barriers E_A come from. Monte Carlo simulations of a strongly interacting model system indicate that E_A of tracer diffusion is strongly affected by memory effects at finite concentrations and low temperatures, where about 10%-50% of E_A comes from the memory contribution which arises from temperature variations in the memory effects and is not thermally activated. It is only the remaining part in E_A which is connected to thermally activated diffusion processes via the average transition rate. In collective diffusion, E_A comes mainly from the temperature dependence of particle number fluctuations, whereas the memory contribution in this case turns out to be less significant,

Wednesday, December 9th 1998, 15:30
Ernest Rutherford Physics Building, room 114