A phase diagram for non-spherical molecules with spherical square wells

Extended law of corresponding states: square-well oblates

The vapour-liquid coexistence collapse in the reduced temperature,T_r=T/T_c, reduced density,ρ_r=ρ/ρ_c, plane is known as a principle of corresponding states, and Noro and Frenkel have extended it for pair potentials of variable range. Here, we provide a theoretical basis supporting this extension, and show that it can also be applied to short-range pair potentials where both repulsive and attractive parts can be anisotropic. We observe that the binodals of oblate hard ellipsoids for a given aspect ratio (κ= 1/3) with varying short-range square-well interactions collapse into a single master curve in theΔB2*-ρ_rplane, whereΔB2*=(B2(T)-B2(Tc))/v0,B₂is the second virial coefficient, andv₀is the volume of the hard body. This finding is confirmed by both REMC simulation and second virial perturbation theory for varying square-well shells, mimicking uniform, equator, and pole attractions. Our simulation results reveal that the extended law of corresponding states is not related to the local structure of the fluid.