Ab Initio Interatomic Potentials and the Classical Molecular Simulation Prediction of the Thermophysical Properties of Helium.

Abstract

The ability of modern ab initio potentials to predict the thermophysical properties of helium is investigated. A new interatomic potential for helium is reported that is based on the latest available ab initio data and that is much more computationally efficient than other ab initio potentials, without sacrificing accuracy. The role of both two-body and three-body interactions is evaluated using classical Monte Carlo and molecular dynamics simulations. Data are reported for the second virial coefficient, vapor-liquid equilibria, acentric factor, compressibility factor, enthalpy, speed of sound, and isobaric heat capacity. Three-body interactions have a minor influence on the properties of helium with the exception of the estimated critical properties. The influence of quantum particle behavior is relevant at temperatures typically below 200 K. For example, the experimental maximum in the isobaric heat capacities (along isobars) of helium is not observed in the classical simulations and can be attributed to quantum particle behavior. However, above this temperature, helium behaves like a classical fluid and its thermodynamic properties can be adequately predicted by determining only two-body interactions.