Abstract
A model of two interacting lattice gases M and X on two interpenetrating square sublattices is studied. Pairwise nearest neighbor attraction ϕ MX and next nearest neighbor repulsion ϕ XX are considered, the latter being restricted to the X sublattice. By calculating ground-state energies of the relevant lattice gas phases LG, M, X, MX, c(2 × 2) X and c(2 × 2) M 2X, ground-state phase diagrams are constructed. Applying standard Monte Carlo techniques, corresponding phase diagrams for elevated temperatures are obtained and compared to the ground-state phase diagram. The Monte Carlo simulations are performed in the grand canonical ensemble with the chemical potentials μ M, μ X and temperature T as independent variables. A simplified mean-field treatment is presented indicating that the behavior of the M sublattice is related to that of a noninteracting Langmuir gas. X represents a lattice gas with nearest neighbor repulsion between adjacent X adatoms. The phase boundary of the c(2 × 2) ordered lattice gas phases is evaluated and compared to the interface solution by Müller-Hartmann and Zittartz.
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