Phase diagram of the lattice fluid with SRLA-potential on the plane triangular lattice

The lattice system with competing interactions (repulsive between nearest neighbors and attractive between nextnext-nearest neighbors) on a triangular lattice is studied. The possibility of existence of two types of ordered phases in the system is established. The initial lattice was splitted into a system of four identical triangular sublattices to describe the ordered phases. The geometric order parameter of the system is introduced. Using the order parameter, the critical value of the interaction parameter is determined and the phase diagram of the system is constructed. The dependence of the critical parameter of the model on the ratio of intensity of competing interactions is investigated. The simulation data for the chemical potential are compared with the results of the quasichemical approximation. It is shown that the quasichemical approximation results in an adequate assessment of the equilibrium properties of the model in the range of its applicability.

ON THE CONSPICUOUS SEGREGATION BEHAVIOR AT Pt–Rh SURFACES

Phase demixing is evaluated as a possible explanation for the anomalous temperature dependence of the Pt segregation at the Pt 50 Rh 50(511), Pt 25 Rh 75(110) and Pt 25 Rh 75(100) surfaces. Calculations are performed in the quasichemical approximation and a broken bond scheme. Although the calculations based on systematic demixing tend to overestimate the surface enrichment, the qualitative agreement appears to be rather good.