Surface Diffusion and the Phase Diagram of XENON/PLATINUM(111): Theory and Simulation

This thesis consists of two parts. In the first part, a theory for calculating the surface chemical diffusion coefficient of adsorbates strongly bound to localized adsorption sites on a crystal surface is presented. The theory is applied to rectangular, square, and hexagonal lattices. The coefficient is expressed as the product of a transition state theory value that can be calculated by Monte Carlo methods, and a dynamical correction factor that can be calculated by molecular dynamics. The fluctuation properties of the dynamical correction factor are investigated for a simple lattice model. The second part of the thesis consists of the development and investigation of a novel potential energy functional form for the Xe/Pt(111) system. The potential is a sum of pair potentials, and predicts that the binding site for the Xe atom is located in the close-packing geometry. The potential is fit to the experimental binding energy, binding distance, and curvature at the minimum. Then, the corrugation of the potential is adjusted to fit the commensurate-incommensurate phase transition temperature. Molecular dynamics simulations indicate that the resulting potential reproduces many features of the experimental phase diagram including the melting temperature and the correct low temperature structure. It yields the correct long-ranged asymptotic interaction, and, in agreement with experiment, the melting transition is first order while the commensurate-incommensurate transition is second order. Finally, the importance of including a substrate-mediated interaction for the Xe-Xe interaction is demonstrated.