MOLECULAR SIMULATION OF WATER ALONG THE LIQUID VAPOR COEXISTENCE CURVE FROM 25-DEGREES-C TO THE CRITICAL-POINT

Previous work has shown that the simple point-charge (SPC) model can represent the experimental dielectric constant of water. In this work, we present results of Monte Carlo simulations of SPC water in the isothermal-isobaric (NPT) ensemble and in the Gibbs ensemble. Long-range intermolecular interactions are included in these simulations by use of the Ewald summation method. When Ewald sums are used, simulated, uniphase liquid potential energies are slightly lower (in absolute value) than those obtained for a simple spherical cutoff of the intermolecular potential. The coexistence curve of SPC water is obtained from 25 to 300°C. The critical constants of SPC water are estimated by adjusting the coefficients of a Wegner expansion to fit the difference between simulated liquid and vapor orthobaric densities; the estimated critical temperature is 314°C and the estimated critical density is 0.27 g/cm3. © 1990 American Institute of Physics.