A comparison of molecular-based models to determine vapor–liquid phase coexistence in hydrogen fluoride

In this work, we apply the Gibbs–Duhem integration (GDI) technique to obtain the vapor–liquid equilibrium (VLE) properties of hydrogen fluoride according to three potential models. Properties examined include coexistence densities, enthalpy of vaporization, and vapor pressure. The models are representative of the various types of potentials used in simulation studies; namely, a pure pair potential from ab initio studies, an effective pair potential which fits parameters to condensed phase properties, and a semi-empirical pair potential. The effective pair potential was found to be the best performer of the three potentials tested, with semi-quantitative agreement with experiment. The other potentials which, by definition, did not include 3+ body effects performed poorly at most states. The effective pair potential is used to specify parameters in a Statistical Associating Fluid Theory (SAFT) model for hydrogen fluoride (HF). Significant improvement is seen over previous attempts to model HF using SAFT, although shortcomings do remain.