PAIR-CORRELATION FUNCTION IN 2-DIMENSIONAL LATTICE GASES

The pair-correlation function -in two-dimensional lattice gases is com puted by means of three discretized classical equations for the struct ure of liquids: the hypernetted-chain, the Percus-Yevick, and the cros sover integral equations. The equations are numerically solved by an i teration procedure. Two different systems are considered: the Ising-Pe ierls lattice gas with nearest-neighbor interactions and a model for 0 adsorbed on the W(110) surface, in which interactions up to the fourt h neighbors are taken into account. The values of the pair-correlation function for nearest, next-nearest, and next-next-nearest neighbors a re compared with the results of Monte Carlo simulations at four differ ent coverages theta (theta=1/8,1/4,1/2,3/4) as functions of the latera l coupling. It turns out that the crossover integral equation gives th e best agreement with Monte Carlo data in both systems, being accurate especially at low theta, whereas the Percus-Yevick equation fails in a wide range of parameters.