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

ZHDANOV, V. P.; SALES, J. L.; UÑAC, R.O.

SURFACE SCIENCE

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1997 vol. 381 p. 599 - 604

0039-6028

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 tool 1 is the same as that given by the standard model. With decreasing A down to 3 kcal mol 1, the drop in Tc 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.