Interplay between Time-Temperature Transformation and the Liquid-Liquid Phase Transition in Water

Abstract

We study the TIP5P water model proposed by Mahoney and Jorgensen, which is closer to real water than previously-proposed classical pairwise additive potentials. We simulate the model in a wide range of deeply supercooled states and find (i) the existence of a non-monotonic "noseshaped" temperature of maximum density line and a non-reentrant spinodal, (ii) the presence of a low temperature phase transition, (iii) the free evolution of bulk water to ice, and (iv) the timetemperature-transformation curves at different densities. PACS numbers:Much effort has been invested in exploring the overall phase diagram of water and the connection among its liquid, supercooled and glassy states [1,2,3], with particular interest in understanding the origin of the striking anomalies at low temperatures, such as the T -dependence of the isothermal compressibility K T , the constant pressure specific heat C P , and the thermal expansivity α P .The "stability limit conjecture" attributes the increase of the response functions upon supercooling to a continuous re-tracing spinodal line bounding the superheated, supercooled and stretched (negative pressure) metastable states [4]. This line at its minimum intersects the temperature of maximum density (TMD) curve tangentially. More recently, a different hypothesis has been developed, for which the spinodal does not re-enter into the positive pressure region, but rather the anomalies are attributed to a critical point below the homogeneous nucleation line [5]. The TMD line, which is negatively sloped at positive pressures, becomes positively sloped at sufficiently negative pressures and does not intersect the spinodal. A line of first order phase transitions -interpreted as the liquid state analog of the line separating low and high density amorphous glassy phases [3,5] -develops from this critical point.Simulations of supercooled metastable states are possible because the structural relaxation time at the temperatures of interest is several orders of magnitude shorter than the crystallization time. It is difficult, but not impossible [6], to observe crystallization in simulations of molecular models [7] because homogeneous nucleation rarely occurs on the time scales reachable by present day computers. Bulk water simulations have been crystallized by applying a homogeneous electric field [8] or placing liquid water in contact with pre-existing ice [9,10], but spontaneous crystallization of deeply supercooled model water has not been observed in simulations.In contrast, experimental measurements of metastable liquid states are strongly affected by homogeneous nucleation. The nucleation and growth of ice particles from aqueous solution has been extensively studied, and the "nose-shaped" time-temperature-transformation (TTT) curves have been measured [1,11,12]. The nonmonotonic relation between crystallization rate and supercooling depth results from the competition between the thermodynamic driving force for nucleation and the kinetics of growth [1]. Crystallization hinders direct experim...

The puzzling unsolved mysteries of liquid water: Some recent progress

“…What has been proved is that computer simulations using tried and tested models of liquid water confirm the broad features of this phase diagram (see Ref. [12] and references therein). But computer models of water (like computer models of anything) are Current experiments on this problem are of two sorts.…”

“…Next we explore the hypothesis [50] that the observed glass transition in biomolecules [12,[51][52][53][54][55][56][57][58][59][60][61][62][63]71] is related to the liquid-liquid phase transition using MD simulations. Specifically, Kumar et al [50] studied the dynamic and thermodynamic behavior of lysozyme and DNA in hydration TIP5P water, by means of the software package GROMACS [64] for: (i) an orthorhombic form of hen egg-white lysozyme [65] and (ii) a Dickerson dodecamer DNA [66] at constant pressure P ¼ 1 atm, several constant temperatures T, and constant number of water molecules N (NPT ensemble).…”

Crystal nucleation as the ordering of multiple order parameters

“…It was found that ice nucleation occurs when a sufficient number of relatively long-lived hydrogen bonds develop spontaneously at the same location to form a fairly compact initial nucleus. At a high density, crystallization takes place more easily [223]. Ice nucleation was also reported by metadynamics simulations [224] and replica-exchange umbrella sampling [225] in the isothermal-isobaric ensemble; however, the results may depend on the choice of order parameters.…”

Test of classical nucleation theory on deeply supercooled high-pressure simulated silica

“…Refs. [12,13,14,15,16]). Current conventional MD simulations typically are able to study systems of a few thousand molecules over a time scale of tens of nanoseconds.…”