Large di erences in phase behavior of closely related lattice ionic models

A series of closely related lattice restricted primitive ionic models were studied by grand canonical Monte Carlo simulations. The ratio of ionic diameter to lattice spacing, , was assigned integer values from 1 to 5. Our results for the = 1 model provide support for the suggestion of Dickman and Stell that there is a tricritical point involving transitions between a disordered and an antiferromagnetic phase. The = 2 model also has an extensive disorderedantiferromagnetic phase coexistence region. For = 3 to 5 the phase behavior is similar to that of the continuous-space restricted primitive model, with a region of normal vapor-liquid coexistence at low temperatures. Our ndings suggest that there can be large qualitative di erences in the phase behavior of closely related lattice models, but that the appropriate continuous-space limit can be approached by ne discretization of the lattice.