Lattice fluid with attractive interaction between nearest neighbors and repulsive interaction between next-next-nearest neighbors on simple cubic lattice

Abstract

The lattice system with competing interactions (attractive between nearest neighbors and repulsive between next-next-nearest neighbors) on a simple cubic lattice is studied. It is shown that the competing interactions lead to the order-disorder phase transitions. The geometric order parameter for localizing the second-order phase transition points is introduced. With its help the critical value of the interaction parameter was established, and the phase diagram of the system was constructed. An analytical quasi-chemical (QChA) approximation for evaluation of the equilibrium parameters of the system is proposed. The chemical potential, the thermodynamic factor, and the correlation functions are determined both within the framework of the developed approximate approach and as a result of the Monte Carlo simulation of the lattice system. The obtained dependence of the thermodynamic factor of the system on concentration indicates a strong suppression of fluctuations, characteristic for an ordered state. In turn, the complex nature of the concentration dependence of the correlation functions reflecting the structural features of the system demonstrates the important contribution of competing interactions. The proposed analytical approach allows one to correctly describe the qualitative features of the structural properties of systems with competing interactions and can be used to quantify the thermodynamic characteristics of these systems.