Precise simulation of criticality in asymmetric fluids

Extensive grand canonical Monte Carlo simulations have been performed for the hard-core square-well fluid with interaction range b=1.5σ. The critical exponent for the correlation length has been estimated in an unbiased fashion as ν=0.63+/-0.03 via finite-size extrapolations of the extrema of properties measured along specially constructed, asymptotically critical loci that represent pseudosymmetry axes. The subsequent location of the critical point achieves a precision of five parts in 10⁴ for T_c and about 0.3% for the critical density ρ_c. The effective exponents γ⁺_eff and β_eff indicate Ising-type critical-point values to within 2% and 5.6%, respectively, convincingly distinguishing the universality class from the ``nearby'' XY and n=0 (self-avoiding walk) classes. Simulations of the heat capacity C_V(T,ρ) and d²p_σ/dT², where p_σ is the vapor pressure below T_c, suggest a negative but small Yang-Yang anomaly, i.e., a specific-heat-like divergence in the corresponding chemical potential derivative (d²μ_σ/dT²) that requires a revision of the standard asymptotic scaling description of asymmetric fluids.