The change of the structural and thermodynamic properties of water from ambient to supercritical conditions as seen by computer simulations

Results of Monte Carlo simulations with various polarizable potential models and reverse Monte Carlo simulations of water are reported at different thermodynamic state points from ambient to supercritical conditions. It is shown that polarizable potential models can reproduce the change of the experimental partial pair correlation functions of water with the temperature and density considerably better than simple nonpolarizable models. Thus, for instance, only the polarizable models can reproduce the experimentally observed elongation of the hydrogen bonds with increasing temperature and decreasing density. On the other hand, the densities of the polarizable water models decrease unexpectedly fast with increasing temperature, which affects also the reproduction of other thermodynamic properties at states of high pressure and high temperature. In analysing the properties of the hydrogen bonded clusters it is found that the space-filling percolating network of the molecules breaks down around the critical point, although a large number of hydrogen bonds still remain in the system above the critical point.