Study of atom diffusion in a lattice gas model with the non-additive lateral interactions

The behavior of a system of atoms adsorbed on a square lattice is investigated by the Monte Carlo simulations using a lattice gas model with the non-additive lateral interactions between the atoms. Here I consider an approach to the problem of the non-addivity principally different from the approach supposed by Milchev and Binder [1,2]. In the new approach the system of adsorbed atoms is described by a set of electric dipoles. The interaction between the atoms is the dipole-dipole electrostatic repulsion. The non-additivity arises due to the dependence of the dipole moments on the number of atoms which are actually present in the close vicinity of these dipoles. I have derived the analytical expressions for the diffusion coefficients and obtained the coverage dependencies for the tracer, center-of-mass and Fickian diffusion coefficients using the Monte Carlo method. The non-addivity of the lateral interaction results in the instability of the atom distribution over the lattice, which substantially changes the thermodynamics of the atom system. Also, it strongly affects the diffusion of the adsorbed atoms.