ANGULAR-DISTRIBUTION FUNCTIONS AND SPECIFIC LOCAL STRUCTURES IN LIQUID WATER

A method of structural analysis, based on restricted averages of the a ngular pair correlation function, is proposed and applied to liquid wa ter. Minimum free energy paths for a molecule moving in an average loc al structure are obtained. Around a central molecule, accepting and do nating neighbors form hydrogen bonds having the same energy minima but differing for the availability of low free energy states. Some bounde d sates have specific bridging functions and connect hydrogen-bond and transition states along negative free energy pathways, thus favoring local diffusion. Bridging and transition states play the role of struc tural defects and include bifurcated hydrogen-bond and interstitial wa ter geometries. Our methods and results can be relevant to understand, from a structural point of view, the anomalous behavior of stressed a nd confined water. (C) 1997 American Institute of Physics. [S0021-9606 (97)50547-2].