Integral equation predictions of liquid state structure for waterlike intermolecular potentials

An application of our recently developed extended RISM equation formulation to several three-site models of water is presented. The site-site correlation functions are obtained and compared to available computer simulation results. Further, the variation of liquid state structure with the model site charge is examined. The analysis of these results has demonstrated that the integral equation approach provides a correct qualitative description of the liquid structure, although the amplitudes of most structural features are somewhat less accurate that their positions. Comparison to our earlier results for simpler models suggests that the nature of the quantitative deficiencies of the approach is predictable. The charging study has shown that the development of waterlike structure with increasing site charge follows a qualitatively different pattern for oxygen-oxygen pairs, compared to those involving hydrogen. This is attributed to interference between the amplitudes characteristic of liquid water and of simple liquids. These results suggest that this is the origin of a relatively flat 0-0 correlation function for several models studied in the past, and, further, that such results should not be properly characterized as "unstructured."