Molecular simulation of orthobaric isochoric heat capacities near the critical point

A molecular simulation strategy is investigated for detecting the divergence of the isochoric heat capacity (C_{V}) on the vapor and liquid coexistence branches of a fluid near the critical point. The procedure is applied to the empirical Lennard-Jones potential and accurate state-of-the-art ab initio two-body and two-body + three-body potentials for argon. Simulations with the Lennard-Jones potential predict the divergence of C_{V}, and the phenomenon is also observed for both two-body and two-body + three body potentials. The potentials also correctly predict the crossover between vapor and liquid C_{V} values and the subcritical liquid C_{V} minimum, which marks the commencement C_{V} divergence. The effect of three-body interactions is to delay the onset of divergence to higher subcritical temperatures.