THE STATIC DIELECTRIC-CONSTANT OF WATER AT PRESSURES UP TO 20 KBAR AND TEMPERATURES TO 1273-K - EXPERIMENT, SIMULATIONS, AND EMPIRICAL EQUATIONS

The static dielectric constant of water was calculated by molecular dy namics simulations using the SPC/E water model up to 1273 K and pressu res to 20 kbar. Simulations within the pressure-temperature range (up to 5 kbar and 823 K) of the available experimental data yield dielectr ic constant (epsilon) in very good agreement with experiment (within 5 %) for all values of density less-than-or-equal-to 1.0 g/cm3. This dem onstrates that the SPC/E model provides a valid means of obtaining the dielectric constant beyond the P, T range of the available data. Seve ral previous attempts were made to extrapolate the experimental values of epsilon to high P, T conditions using semi-empirical fit equations . We tested two of these equations (Pitzer, 1983; Franck et al., 1990) against our simulated values of epsilon at densities of 0.322, 0.5 g/ cm3 and 1.0 g/cm3 for temperatures ranging from 600-1200 K. For densit y less-than-or-equal-to 1 g/cm3 and temperatures above 600 K the equat ion of Franck et al. (1990) is in agreement with the simulations to wi thin 7% and provides, therefore, a simple and valid method of extrapol ation of the data.