Large Lattice Discretization Effects on the Phase Coexistence of Ionic Fluids

We examine the phase behavior of lattice restricted primitive models for integer values of the ratio of ionic diameter to lattice spacing, $\xi$. For $\xi \le 2$, there is coexistence between a disordered phase and an antiferromagnetic phase, but no vapor-liquid equilibrium. For $\xi \ge 3$, a region of normal vapor-liquid coexistence is found, with critical temperatures and densities which are very close to their continuous space counterparts. Our findings stress that lattice structure can result in qualitatively different physics from continuous space models, but that the two models converge even for relatively coarsely discretized lattices.