Fluid coexistence close to criticality: scaling algorithms for precise simulation

The algorithm has been applied to simulation data for a hard-core square-well fluid and the restricted primitive model electrolyte for sizes up to L/a=8-12 (where a is the hard-core diameter): the coexistence curves can be computed to a precision of ±1-2% of ρc up to |T−Tc|/Tc=10−4 and 10−3, respectively. Universality of the scaling functions and the exponent β is verified and the (Tc,ρc) estimates confirm previous values based on data from above Tc. The algorithm extends directly to calculating the diameter, ρdiam(T)≡12(ρ++ρ−), and can lead to estimates of the Yang-Yang ratio. Furthermore, a new, explicit approximant for the basic scaling function Y permits straightforward estimates of Δρ∞(T) from limited Q-data when Ising-type criticality may be assumed.