Discretization Dependence of Criticality in Model Fluids: a Hard-core Electrolyte

Grand canonical simulations at various levels, $\zeta =5$-20, of fine- lattice discretization are reported for the near-critical 1:1 hard-core electrolyte or RPM. With the aid of finite-size scaling analyses it is shown convincingly that, contrary to recent suggestions, the universal critical behavior is independent of $\zeta$ $(\text{grtsim}4)$; thus the continuum $(\zeta \to \mathrm{\infty })$ RPM exhibits Ising-type (as against classical, SAW, XY, etc.) criticality. A general consideration of lattice discretization provides effective extrapolation of the {\em intrinsically} erratic $\zeta$-dependence, yielding $({\text{Tc}}^{\ast },{\text{rhoc}}^{\ast })\simeq ({0.0493}_3,0.075)$ for the $\zeta =\mathrm{\infty }$ RPM.