Engineering a molecular model for water phase equilibrium over a wide temperature range

Abstract

The pure water phase equilibrium is calculated over a wide temperature range using the Gibbs ensemble Monte Carlo method with simple two-body molecular models. The Ewald summation method is used to account for the long-range Coulombic interactions. Coexisting liquid and vapor densities and vapor pressure at different temperatures are calculated explicitly. A new expression is developed for the direct calculation of pressure suitable for systems where the Ewald method is used. To improve agreement with experimental data, a simple scaling procedure is proposed that allows reparametrization of the molecular models without the need for additional calculations. Critical constants, second virial coefficient, and heat of vaporization are calculated from the different models. Finally, water structure is examined at low and high temperature. In all cases, comparison with experimental data is shown.