CO Adsorption-Induced Surface Segregation and Formation of Pd Chains on AuPd(100) Alloy: Density Functional Theory Based Ising Model and Monte Carlo Simulations

摘要

In order to study how adsorption of CO molecules changes the surface composition of AuPd alloys, we develop a theoretical methodology which is able to take this effect into account. An Ising model based on density functional theory calculations is derived to define interatomic potentials that describe metal-metal, metal-CO, and CO-CO interactions. Then, through the use of Monte Carlo simulations within the semi-grand canonical ensemble, the effect of adsorption-induced segregation for the AuPd(100) surface is well-reproduced for different temperatures and CO pressures. Segregation isotherms identify a Pd surface enrichment for low CO pressures, and CO surface saturation is reached at an intermediate coverage of theta = 0.5 ML. Furthermore, Pd chains induced by an ordering of adsorbed CO molecules appear at low temperature and intermediate CO pressures. These chains are the result of a competitive effect between CO-CO repulsions and metal-CO interactions.