Monte Carlo Simulation Methods for Computing Liquid–Vapor Saturation Properties of Model Systems

We discuss molecular simulation methods for computing the phase coexistence properties of complex molecules. The strategies that we pursue are histogram-based approaches in which thermodynamic properties are related to relevant probability distributions. We first outline grand canonical and isothermal-isobaric methods for directly locating a saturation point at a given temperature. In the former case, we show how reservoir and growth expanded ensemble techniques can be used to facilitate the creation and insertion of complex molecules within a grand canonical simulation. We next focus on grand canonical and isothermal-isobaric temperature expanded ensemble techniques that provide a means to trace saturation lines over a wide range of temperatures. To demonstrate the utility of the strategies introduced here, we present phase coexistence data for a series of molecules, including n-octane, cyclohexane, water, 1-propanol, squalane, and pyrene. Overall, we find the direct grand canonical approach to be the most effective means to directly locate a coexistence point at a given temperature and the isothermal-isobaric temperature expanded ensemble scheme to provide the most effective means to follow a saturation curve to low temperature.