Predicting order-disorder phase transitions of O/Pd(111) from ab initio Wang-Landau Monte Carlo calculations

We study the O/Pd 111 system using a lattice-gas Hamiltonian where the many-body interactions among the oxygen adsorbates are derived from a series of density-functional-theory calculations. Through Monte Carlo simulations that employ the Wang-Landau algorithm, we use this Hamiltonian to predict the order-disorder phase-transition temperature as a function of oxygen coverage. We find that oxygen forms ordered p 2 2 , 3 3 R30° and p 2 1 structures, in agreement with the zero-temperature convex hull, which undergo a continuous transition to a disordered phase upon increasing the temperature. The transition temperature versus coverage curve displays peaks around the coverages corresponding to the formation of the p 2 2 and p 2 1 ordered structures, similar to what has been found from experimental and theoretical studies of the O/Pt 111 and O/Ru 0001 systems.