Simulations of the order-disorder phase transition and thermal desorption on a square lattice beyond the lattice-gas approximation

Abstract

Employing Monte Carlo simulations, we calculate a phase diagram and thermal desorption spectra for adsorption on a square lattice in the framework of the model taking into account the shifts of chemisorbed particles from equilibrium positions. At realistic values of the activation barrier for surface diffusion, A = 3−20 kcal mol −1, the results obtained are surprisingly close to those predicted by the standard lattice-gas model. In particular, the critical temperature, T c, for the order-disorder phase transition calculated for A = 20 kcal mol −1 is the same as that given by the standard model. With decreasing A down to 3 kcal mol −1, the drop in T c is only ⋍ 10%. In the thermal desorption spectra, the decrease of A results in decreasing the maximum intensity of the low-temperature peak, but this effect is rather weak.