The role of three-body interactions on the equilibrium and non-equilibrium properties of fluids from molecular simulation

The aim of this work is to use molecular simulation to investigate the role of three-body interatomic potentials in noble gas systems for two distinct phenomena: phase equilibria and shear flow. In particular we studied the vapour-liquid coexisting phase for pure systems (argon, krypton and xenon) and for an argon-krypton mixture, utilizing the technique called Monte Carlo Gibbs ensemble. We also studied the dependence of the shear viscosity, pressure and energy with the strain rate in planar Couette flow, using a non-equilibrium molecular simulation (NEMD) technique. The results we present in this work demonstrate that three-body interactions play an important role in the overall interatomic interactions of noble gases. This is demonstrated by the good agreement between our simulation results and the experimental data for both equilibrium and non-equilibrium systems. The good results for vapour-liquid coexisting phases encourage performing further computer simulations with realistic potentials. This may improve the prediction of quantities like critical temperature and density, in particular of substances for which these properties are difficult to obtain from experiment. We have demonstrated that use of accurate two- and three-body potentials for shearing liquid argon and xenon displays significant departure from the expected strain rate dependencies of the pressure, energy and shear viscosity. For the first time, the pressure is convincingly observed to vary linearly with an apparent analytic y2 dependence, in contrast to the predicted y3/2 dependence of mode -coupling theory. Our best extrapolation of the zero -shear viscosity for argon gives excellent agreement (within 1%) with the known experimental data. To the best of our knowledge, this the first time that such accuracy has been achieved with NEMD simulations. This encourages performing simulations with accurate potentials for transport properties.