THE STATIC DIELECTRIC-CONSTANT OF SPC AND TIP4P WATER BY PERTURBATION-THEORY

A second-order perturbation theory that was previously applied to hard-sphere-dipolar and Stockmayer fluids is extended to molecules with spherical cores and discrete point charge distribution of arbitrary symmetry. We use a recently published improvement on the Kirkwood superposition approximation for the reference state triplet distribution function, and we apply the theory to obtain the static dielectric constant (epsilon) of SPC and TIP4P water at approximately 1 gm cm-3 and a range of temperatures. By comparison with the results of simulations on these models we find that the theory works up to y congruent-to 3 (where y is the dipolar strength function) but overestimates epsilon beyond y congruent-to 3. y less than or similar 3 is also the range of validity of the theory when applied to a Stockmayer fluid, but for the latter the theory underestimates epsilon for y greater than or similar to 3. We physically interpret our results for the angular correlation parameter (G) by reference to structures that are believed to be important in real water and in dense dipolar fluids.