Analysis of the hydrogen-bonded structure of water from ambient to supercritical conditions

The structure of water has been analyzed at eight different thermodynamic states from ambient to supercritical conditions both by molecular dynamics (MD) and Reverse Monte Carlo (RMC) simulation. MD simulations have been carried out with two different potential models, a polarizable potential and one of the most successful nonpolarizable models, i.e., the well known Simple Point Charge potential in its revised version labeled by $E$ (SPC/E). It has been found that, although the polarizable model can reproduce the experimental partial pair correlation functions at the high temperature states better than the nonpolarizable one, it still cannot account for all the features of the measured functions. The experimental partial pair correlation functions have been well reproduced by the RMC simulations at every state point. The resulting structures have been analyzed in detail. It has been found that the tetrahedral orientation of the hydrogen bonded neighbors is already lost at 423k, whereas the hydrogen bonds themselves remain preferentially linear even above the critical point. In investigating the properties of the hydrogen-bonded clusters of the molecules it has been found that the space-filling percolating network, present under ambient conditions, collapses around the critical point.