Molecular Simulation of Phase Equilibria

This chapter presents an introduction to the rapidly expanding field of molecular simulation methodologies for calculations of fluid-phase coexistence, with particular emphasis on high pressure and supercritical systems. The first part of the chapter deals with methodological issues. The focus is on Monte-Carlo techniques for the determination of free energies and phase equilibria. Particle insertion techniques are first briefly discussed. The Gibbs ensemble Monte Carlo method is then covered in detail. While the original method is applicable primarily to simple model potentials, recently developed configurational-bias sampling techniques allow the study of a broad range of systems. The second part of the chapter reviews applications of molecular simulation techniques to systems of interest for supercritical processes. Phase diagrams of pure components, including water, hydrocarbons, ionic and polymeric fluids are first discussed. Studies of simple mixtures reveal that conformal solution theories have a significantly greater range of applicability than previously thought. The chapter concludes with a discussion of the future promise and limitations of molecular simulation techniques for the study of fluid phase equilibria.