Eutectic point in a simple lattice gas model

We investigate the phase diagram and the critical properties of the adsorbate system sulphur/ruthenium(0001) in the coverage region 1 < � < 1 by means of Monte-Carlo simulations of a simple lattice gas model on a triangular lattice. The model contains only repulsive nearest and next-nearest neighbor interactions. Combining results obtained by using both Glauber and Kawasaki kinetics in the simulations we identify two tricritical points, three coexistence regions and a eutectic point in the phase diagram of the system. Our results agree with the findings of recent experimental work on S/Ru(0001). Furthermore we are able to add certain details to the experimentally observed phase diagram. PACS 0550 - Lattice theory and statistics; Ising problems PACS 6470 - Phase equilibria, phase transitions, and critical points The comparison of experimental phase diagrams and of experimental data for the critical properties of adsorbed layers with the results of computer simulations of appropriate lattice gas models can provide detailed information about the effective lateral interactions between the adsorbed particles. However, the reliability of this method depends on the validity of the lattice gas description for the system to be considered. Therefore, this point requires careful experimental tests. The inadequacy of the lattice gas description may be the reason for the quantitative disagreement between the simulated [1] and the experimental [2] phase diagrams of some systems.