Seven-Site Effective Pair Potential for Simulating Liquid Water

Constant pressure simulations were carried out to construct a new rigid nonpolarizable seven-site water model (TIP7P), which is an effective and efficient version of flexible seven-fluctuating-charge water model. In this model, the positive charges are located on three nuclei and the negative charges disperse on two bond sites at the geometric center of each OH bond and two lone-pair sites along the tetrahedral direction away from the oxygen atom. Our new model performs better than other models in properties, such as radial distribution function, liquid density, thermal expansion coefficient, isothermal compressibility, vaporization enthalpy, isobaric heat capacity, static dielectric constant, self-diffusion coefficient, critical temperature, and density. This model reproduces liquid density and static dielectric constant over the temperatures from 253 to 373 K at 1 atm with the standard deviation of 0.0010 g/cm³ and 1.37 to the experimental data, respectively. The maximum density is 1.0006 g/cm³ at 277 K. The calculated isobaric compressibility presents a minimum at about 310 K close to the experimental value of 319 K. The self-diffusion coefficient agrees the experimental data with the standard deviation of 0.55 × 10^-5 cm²/s, although it is not the target property for parameterization. Liquid-vapor phase equilibrium was examined in slab simulations. The evaluated critical temperature and density are 633 K and 0.337 g/cm³ close to the experimental values of 647.096 K and 0.322 g/cm³. This model also presents reasonable vaporization enthalpy and isobaric heat capacity. Based upon good performances mentioned, our new model is a good choice for more accurate investigation to large molecular systems.