Fourth and Fifth Virial Coefficients of Polarizable Water

We report values of the virial coefficients B-4 and B-5 for the Gaussian charge polarizable model (GCPM) of water using the overlap-sampling implementation of Mayer sampling molecular simulation. These results supplement values for the lower-order coefficients B-2 and B-3 reported previously, and in the present work, we provide more precise values of these coefficients as well. The precision of all virial coefficients is such that the standard error in the calculated pressure is significantly less than 1% for most temperatures, with the exception of temperatures near the critical, where the error approaches 100% at the critical density, and supercritical, where the uncertainty in B-5 introduces an error of about 5% in the pressure at the critical density. We examine these coefficients in the context of the equation of state and molecular clustering. Comparisons are made to established molecular simulation data, quantum chemical calculations, and experimental data for real water. Over both sub- and supercritical temperatures, the virial series to B-5 is accurate for densities only up to about half the critical density. In this regime, deviation is observed from experimental data for real water, and it is suggested that further development of the model might do well to further improve the relatively good agreement it has with the experimental second virial coefficient of water. The virial coefficients are used to characterize molecular clusters (dimers through pentamers) in GCPM water under supercritical and saturated vapor conditions between 210 and 673 K.