Static and dynamic properties of stretched water

Abstract

We present the results of molecular dynamics simulations of the extended simple point charge model of water to investigate the thermodynamic and dynamic properties of stretched and supercooled water. We locate the liquid-gas spinodal, and confirm that the spinodal pressure increases monotonically with T, supporting thermodynamic scenarios for the phase behavior of supercooled water involving a ''non-reentrant'' spinodal. The dynamics at negative pressure show a minimum in the diffusion constant D when the density is decreased at constant temperature, complementary to the known maximum of D at higher pressures. We locate the loci of minima of D relative to the spinodal, showing that the locus is inside the thermodynamically metastable regions of the phase diagram. These dynamical results reflect the initial enhancement and subsequent breakdown of the tetrahedral structure and of the hydrogen bond network as the density decreases.

Thermodynamic and dynamic anomalies for a three-dimensional isotropic core-softened potential

“…The continuity of the force is similar that one expect for realistic systems. We studied the density anomaly The studied continuous core-softened potential, despite of not having long-ranged or H-bond-like directional interactions, exhibit thermodynamic and dynamic anomalies similar to the ones observed in SPC/E water [10].…”

“…(5). The region of diffusion anomalies (T Dmax , P Dmax ) and (T Dmin , P Dmin ) lies outside the region of density anomalies like in SPC/E water [10].…”

“…This type of potential gives a distribution function similar to the one expected for SPC/E water [40]. We check if the region in the pressure-temperature phase-diagram of thermodynamic anomalies is inside the region of dynamic anomalies as in SPC/E water [10].…”

“…In SPC/E water, the region of the pressure-temperature (p -T) phase-diagram where the density anomaly appears is contained within the region of the p -T phase-diagram where anomalies in the diffusivity are present [9,10].…”

“…Besides, in a certain range of pressures, also exhibits an anomalous increase of compressibility and specific heat upon cooling [2]- [4]. Far less known are its dynamics anomalies: while for most materials diffusivity decreases with increasing pressure, liquid water has an opposite behavior in a large region of the phase diagram [5,6,7,8,9,10,11,12,13]. The increase of diffusivity of water as the pressure is increased is related to the competition between the local ordered tetrahedral structure of the first neighbors and the distortions of the structure of the first and second neighbors.…”