Revised TIPS for simulations of liquid water and aqueous solutions

An intermolecular potential function for the water dimer (TIPS2) has been developed and used in Monte Carlo simulations of liquid water in the NPT ensemble at 1 atm and −30, 25, and 75 °C. A simple four-site model is employed for the monomers with one Lennard-Jones term acting between oxygens and Coulomb terms for the intermolecular interactions between the charged sites. The function yields excellent thermodynamic results for the liquid across the temperature range; the average error in the computed densities and energies is 1.2% and a temperature of maximum density is indicated in the vicinity of 25 °C. Futhermore, the structural results are in reasonable agreement with Narten’s x-ray data. Specifically, the oxygen–oxygen radial distribution function shows three well-resolved peaks at 25 °C and a reduction in structure with increasing temperature. The simplicity of the TIPS2 potential,its success in describing liquid water, and the availability of TIPS parameters for hydrocarbons and for various organic functional groups provide a framework for computer simulations of aqueous solutions.