Free energy of mixing, phase stability, and local composition in Lennard-Jones liquid mixtures

By the use of umbrella-sampling technique in the Monte Carlo method proposed by Torrie and Valleau, reliable data have been established for the Helmoholtz free energy of mixing in some selected models of Lennard-Jones liquid mixtures. The variational method in perturbation theory is found to account for these Monte Carlo data. Validity of some representative semiempirical theories is discussed and it is found that none of them can reproduce the present Monte Carlo results reasonably well. Finally the phase stability of the present models is discussed in terms of both the free energy of mixing and local composition values recently obtained from our molecular dynamics calculations.