Thermodynamic properties of water from combined quantum and statistical mechanics in the temperature range from 273.16 to 423.15 K

Abstract

A combined integral equation and quantum mechanical method, the so-called RISM–SCF method, is used to develop a self consistent effective potential model to describe pure liquid water in accordance with thermodynamic properties like chemical potential or entropy over a wide range of temperature and pressure. Since the thermodynamic excess properties calculated with the SSOZ equation are extremely charge dependent using constant Lennard–Jones parameters, we first developed a new function of the Lennard–Jones parameters of water depending on the partial charges taking into account the charge dependent polarisation which is reflected mainly by the attracting term of the Lennard–Jones potential. We used experimental data of thermodynamic excess functions at three selected temperatures in order to adjust the potential parameters reproducing these thermodynamic functions with an error smaller than 3%. Using this charge dependence of the Lennard–Jones parameters we applied the RISM–SCF method to calculate thermodynamic properties of pure liquid water, especially its vapor pressure, in a temperature range from 273.16 to 423.15 K and a pressure range from 0.5 to 500 kPa. Our calculated values of the vapor pressure agree well with the experimental data, as do our values of chemical potential and entropy as function of temperature.