Ordering in lattice gases with competing interactions on interpenetrating square sublattices

Abstract

We study a model of interacting lattice gases M and X on two interpenetrating square sublattices with nearest neighbor attaction ϕMX and next nearest neighbor repulsion ϕXX in the X sublattice. By calculating ground-state energies of the relevant lattice gas phases LG, M, X, MX,c(2×2) X andc(2×2) M2X we obtain ground-state phase diagrams for various values of R ≡ ϕXX/ϕMX. Standard Monte Carlo simulation techniques are applied to investigate the lattice gas models at nonzero temperatures for the caseR=−0.5. The simulations are performed in the grand canonical ensemble with the chemical potentials μM, μX and temperatureT as independent variables. From adsorption isotherms θM (μM, μX) and θX (μM, μX) various phase transition, of first and second order between different lattice gas phases are identified. We calculate phase diagrams for the caseR=−0.5, which are compared to corresponding phase diagrams forR=0 andR=−1. Finally we discuss the applicability of such lattice gas models for the description of cosegregation processes.