Critical and glassy behavior in models of supercooled water.

摘要

A computational study of liquid water is performed to test the hypothesis that a novel critical point, {dollar}Cspprime,{dollar} exists in the supercooled region of the phase diagram. Molecular dynamics simulations are developed to extend the equation of state for two widely used pair potentials to study the liquid behavior near {dollar}Cspprime.{dollar} Apparent divergences in the isothermal compressibility are studied. Evidence for a liquid-liquid phase transition is presented, indicating both phase separation and the existence of a van der Waals loop in the pressure as a function of volume. The equation of state in the two models is used to set bounds on the properties of supercooled water.; The transport properties are found to agree with predictions made by mode coupling theory for the ideal glass transition. Specifically a power-law dependence of the diffusion constant, D, on the reduced temperature, {dollar}(T-Tsb{lcub}s{rcub})/Tsb{lcub}s{rcub},{dollar} is found, where {dollar}Tsb{lcub}s{rcub}{dollar} is the temperature of structural arrest. It is found that {dollar}Tsb{lcub}s{rcub}{dollar} is pressure dependent over a large range of pressures and that {dollar}Tsb{lcub}s{rcub}>Tsb{lcub}Cspprime{rcub}.{dollar} The pressure dependence of {dollar}Tsb{lcub}s{rcub}{dollar} is found to be consistent with the two amorphous glassy phases of water, low density amorphous water (LDA) and high density amorphous water (HDA). For {dollar}T