Equilibrium and diffusion properties of two-level lattice systems: Quasi-chemical and diagrammatic approximation versus Monte Carlo simulation results

The quasi-chemical and diagrammatic approximations are generalized for two-level lattice gas systems that are considered as models of intercalation compounds. The role of interparticle interactions is investigated. Monte Carlo simulation are used to demonstrate that the diagrammatic approximation represents well such equilibrium and structural lattice gas properties as the chemical potential isotherms, phase transition diagram, the thermodynamic factor (or chemical capacitance) and the probability for nearest neighbor sites to be occupied. Simpler quasi-chemical approximation can be used when semiquantitative results are of interest. Diffusion properties are investigated by means of Monte Carlo simulations.