Vapour liquid equilibria of Lennard-Jones model mixtures from the NpT plus test particle method

The NpT+test particle method for the calculation of vapour liquid phase equilibria (VLE) is applied to ten binary Lennard-Jones mixtures which were studied previously with the Gibbs ensemble (Harismiadis et al., 1991). The present method uses one simulation for the description of the liquid. For the vapour two simulations are required at higher densities, whilst at lower vapour densities the Haar-Shenker-Kohler (HSK) equation of state is used. The chemical potentials from simulation are calculated by Widomʹs test particle insertion method (Widom, 1963) and adjusted with the results from the particle swap method, which yields the differences of the chemical potentials. Additionally, VLE results are obtained by using the Fischer-Lago-Bohn perturbation theory for the liquid and the HSK equation for the vapour. A comparison of the new simulation results with those of the Gibbs ensemble shows qualitative agreement but in most cases smaller error bars and considerably less scatter of the present data. Moreover, the simulations confirm the good to excellent performance of the perturbation theory.