ENGINEERING A MOLECULAR-MODEL FOR WATER PHASE-EQUILIBRIUM OVER A WIDETEMPERATURE-RANGE

The pure water phase equilibrium is calculated over a. wide temperatur e range using the Gibbs ensemble Monte Carlo method with simple two-bo dy molecular models. The Ewald summation method is used to account for the long-range Coulombic interactions, Coexisting liquid and vapor de nsities and vapor pressure at different temperatures are calculated ex plicitly. A new expression is developed for the direct calculation of pressure suitable for systems where the Ewald method is used. To impro ve agreement with experimental data, a simple scaling procedure is pro posed that allows reparametrization of the molecular models without th e need for additional calculations. Critical constants, second virial coefficient, and heat of vaporization are calculated from the differen t models. Finally, water structure is examined at low and high tempera ture. In all cases, comparison with experimental data is shown.