6533b853fe1ef96bd12ac9e4

RESEARCH PRODUCT

Monte Carlo studies of adsorbed monolayers: Lattice-gas models with translational degrees of freedom

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Standard lattice-gas models for the description of the phase behavior of adsorbed monolayers are generalized to ``elastic lattice gases'' which allow for translational degrees of freedom of the adsorbate atoms but have the substrate lattice structure built into the adsorbate-adsorbate interaction. For such models, we derive a simple and efficient grand-canonical Monte Carlo algorithm, which treats the occupied and empty sites in precisely the same way. Using this method, we calculate the phase diagram of a simple model for the adsorption of hydrogen on palladium (100); this model includes only pairwise interactions and exhibits an ordered $c(2\ifmmode\times\else\texttimes\fi{}2)$ structure. For our choice of parameters, we find only a rather small influence of the translational degrees of freedom on the phase diagram. In particular, the observed asymmetry, albeit clearly present, is quite weak. Finite-size scaling reveals that the second-order phase transition between $c(2\ifmmode\times\else\texttimes\fi{}2)$ and the disordered phase is Ising-like, i.e., the elastic degrees of freedom do not change the universality class.