Dynamic Crossover and Liquid-liquid Critical Point in the Tip5p

Water is hypothesized to have a low temperature phase transition line which separates a high density water at high temperatures from a low density water at low temperatures. This negatively sloped first order liquid-liquid phase coexistence line terminates at a critical point known as the liquid-liquid critical point. This critical point is hypothesized to exist in a deeply supercooled region of the phase diagram of water. Recent experiments have given an indirect indication of this phase transition. Neutron scattering and NMR experiments on water confined in hydrophilic nanopores revealed that the dynamics of water changes from the dynamics of a high density liquid (nonArrhenius) at high temperatures to that of a low density liquid (Arrhenius) at low temperatures. Motivated by these experiments we investigated the TIP5P model of water. We find that the dynamic transition appears to be related to crossing the specific heat maxima line (Widom line) which emanates from the liquidliquid critical point. Moreover, we find that water not only undergoes a dynamical change but also structural changes on crossing the Widom line. The structure of the liquid changes from a high density liquid to a low density liquid.