Influence of obstacles on equilibrium properties of the lattice fluid on a surface

The model of the lattice fluid on the square lattice with blocked sites (obstacles) and attractive or repulsive nearest neighbor interactions is considered. The simple quasi-chemical approximation (QChA) for the free energy of the lattice system is proposed. The expressions for the chemical potential, thermodynamic factor and distribution functions are obtained in a closed form. The method is generalized on the lattice systems in which the order-disorder phase transition can exist. The algorithm of the Monte Carlo simulation of the lattice system with blocked sites is proposed. It is shown that the critical temperature linearly increases with the concentration of blocked sites. The simulation data are compared with the results of QChA. It is shown that QChA provides with reasonable semiquantitative results for the studied systems and can be used as the basis for next order approximations.