The lattice fluid with the competing interactions on the square lattice

Abstract

The lattice system with competing interactions (attractive between nearest neighbors and repulsive between fourth order neighbors) on a square lattice is studied. It is shown that the competing interactions lead to the order-disorder phase transitions. The possibility of existence of two types of ordered phases in the system is established and investigated the conditions for the occurrence of each of these phases. The geometric order parameter for localizing the structural phase transition points is proposed. With its help, the critical value of the interaction parameter was established, and the dependence of the critical temperature of the model versus the ratio of intensities of competing interactions was studied. The Monte Carlo simulation data are compared with the results of the quasi-chemical approximation. It is shown that the quasi-chemical approximation allows one to determine the thermodynamic properties of the model with high accuracy.