Entropy from Correlations in TIP4P Water.

We use molecular dynamics to compute the pair distribution function of liquid TIP4P water as a function of the intermolecular distance and of the five angles that are needed to specify the relative position and orientation of two water molecules. We also calculate the translational and orientational contributions to the two-body term in the multiparticle correlation expansion of the configurational entropy at three selected thermodynamic states, where we also test various approximations for the angular dependence of the pair distribution function. We finally compare the results obtained for the pair entropy of TIP4P water with the experimental values of the excess entropy of ordinary water.