Thermodynamic Properties of the System with Competing Interactions on a Triangular Lattice

The system that models biological objects (e.g. colloids, ensembles of protein molecules) with competing interactions is considered. Such objects attract each other on short distances and repel at larger separations. The model is the system of particles on a triangular lattice interacting via a pair potential which is attractive for the nearest neighbors and repulsive for the third ones. Monte Carlo simulation data for the chemical potential, thermodynamic factor and correlation functions indicate the possibility of order-disorder phase transitions in this system. The simulation data are compared with the analytical results on the basis of the quasichemical approximation.