Search

Supercooled water exhibits a breakdown of the Stokes-Einstein relation between the diffusion constant D and the alpha relaxation time [[tau].sub.[alpha]]. For water simulated with two different potentials, TIP5P and ST2, we find that the temperature of the decoupling of diffusion and alpha relaxation correlates with the temperature of the maximum in specific heat that corresponds to crossing the Widom line [T.sub.w](P). Specifically, we find that our results for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.]/T collapse onto a single 'master curve' if temperature is replaced by T-[T.sub.w](P). We further find that the size of the mobile molecule clusters (dynamical heterogeneities) increases sharply near [T.sub.w](P). Moreover, our calculations of mobile particle cluster size [(n(t*).sub.w] for different pressures, where t* is the time for which the mobile particle cluster size is largest, also collapse onto a single master curve if T is replaced by T-[T.sub.w](P). The crossover to a more locally structured low density liquid (LDL) as T [right arrow] [T.sub.w](P) appears to be well correlated both with the breakdown of the Stokes-Einstein relation and with the growth of dynamic heterogeneities. Our results are consistent with the possibility that the breakdown of the SE relation in supercooled water at low pressures is associated with the hypothesized liquid-liquid phase transition. liquid-liquid phase transition in water | transport properties of water | dynamic heterogeneities

We investigate, for two water models displaying a liquid--liquid critical point, the relation between changes in dynamic and thermodynamic anomalies arising from the presence of the liquid--liquid critical point. We find a correlation between the dynamic crossover and the locus of specific heat maxima [C.sup.max.sub.p] ('Widom line') emanating from the critical point. Our findings are consistent with a possible relation between the previously hypothesized liquid-liquid phase transition and the transition in the dynamics recently observed in neutron scattering experiments on confined water. More generally, we argue that this connection between [C.sup.max.sub.p] and dynamic crossover is not limited to the case of water, a hydrogen bond network-forming liquid, but is a more general feature of crossing the Widom line. Specifically, we also study the Jagla potential, a spherically symmetric two-scale potential known to possess a liquid-liquid critical point, in which the competition between two liquid structures is generated by repulsive and attractive ramp interactions. liquid--liquid critical point | low-density liquid | high-density liquid | [C.sup.max.sub.p] line | [K.sup.max.sub.T] line