Combination of monovalent and divalent sites on an associating species: Application to water

This contribution is in honor of Professor Keith E. Gubbins, an international leader in developing advances in statistical mechanics and molecular simulation for engineering applications. The research presented here extends the SAFT model that Chapman proposed and developed while a graduate student with Professor Gubbins. In this manuscript, a thermodynamic perturbation theory within a multi-density formalism framework is extended to model species with a combination of monovalent and divalent association sites. Theory predictions are verified with Monte Carlo simulation results for different conditions of temperature, density, and angular size of the divalent site. The theory is applied to model water, where the two lone pairs of electrons on the oxygen atom are represented with a divalent site that includes cooperative hydrogen bonding. The theory results are in good agreement with experiments for saturated densities, vapor pressure, internal energy, and extent of hydrogen bonding.