Universality Class of Criticality in the Restricted Primitive Model Electrolyte

The 1:1 equisized hard-sphere electrolyte or restricted primitive model has been simulated via grand-canonical fine-discretization Monte Carlo. Newly devised unbiased finite-size extrapolation methods using loci in the temperature-density or (T,ρ) plane of isothermal ρ^2-k vs pressure inflections, of Q≡〈m²〉²/〈m⁴〉 maxima, and of canonical and C_V criticality, yield estimates of (T_c,ρ_c) to ±(0.04,3)%. Extrapolated exponents and Q ratio are (γ,ν,Q_c) = [1.24(3),0.63(3);0.624(2)], which support Ising (n = 1) behavior with (1.23₉,0.630₃;0.623₆), but exclude classical, XY (n = 2), self-avoiding walk (n = 0), and n = 1 criticality with potentials ϕ(r)>Φ/r^4.9 when r→∞.