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

• Published in: Surface science 1997-06, Vol.381 (2), p.L599-L604
• Main Authors: Zhdanov, V.P., Sales, J.L., Un˜ac, R.O.
• Format: Article
• Language: English
• Subjects: Computer simulations; Surface thermodynamics (including phase transitions); Thermal desorption
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/S0039-6028(97)00056-3

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.