Phase diagram of amorphous solid water: Low-density, high-density, and very-high-density amorphous ices

Abstract

We describe the phase diagram of amorphous solid water by performing molecular dynamics simulations using the simple point charge (SPC/E) model. Our simulations follow different paths in the phase diagram: isothermal compression/decompression, isochoric cooling/heating and isobaric cooling/heating. We are able to identify low-density amorphous (LDA), highdensity amorphous (HDA), and very-high density amorphous (VHDA) ices.The density ρ of these glasses at different pressure P and temperature T agree well with experimental values. We also study the radial distribution functions of glassy water. In agreement with experiments, we find that LDA, HDA and VHDA are characterized by a tetrahedral hydrogen-bonded network and that, as compared to LDA, HDA has an extra interstitial molecule between the first and second shell. VHDA appears to have two such extra molecules. We obtain VHDA by isobaric heating of HDA, as in experiment. We also find that 1 "other forms" of glassy water can be obtained upon isobaric heating of LDA, as well as amorphous ices formed during the transformation of LDA to HDA.We argue that these other forms of amorphous ices, as well as VHDA, are not altogether new glasses but rather are the result of aging induced by heating.Samples of HDA and VHDA with different densities are recovered at normal P , showing that there is a continuum of glasses. Furthermore, the two ranges of densities of recovered HDA and recovered VHDA overlap at ambient P . Our simulations are consistent with the possibility of HDA→LDA and VHDA→LDA transformations, reproducing the experimental findings. We do not observe a VHDA→HDA transformation, and our final phase diagram of glassy water together with equilibrium liquid data suggests that for the SPC/E model the VHDA→HDA transformation cannot be observed with the present heating rates accessible in simulations. Finally, we discuss the consequences of our findings for the understanding of the transformation between the different amorphous ices and the two hypothesized phases of liquid water.

First-principles molecular dynamics simulations of MgSiO3 glass: Structure, density, and elasticity at high pressure

“…We find that hot compression produces significantly greater density at the same pressure than cold compression. Similar type of behavior has also been observed in case of amorphous water/ice (Loerting et al 2001;Giovambattista et al 2005). The reason for this is that the high-temperature liquid has access to a wider fraction of configuration space than the low temperature glass and is more readily able to accommodate its structure to high-pressure conditions.…”

The structure of amorphous, crystalline and liquid GeO2

“…Gutierrez and Rogan [119] have simulated GeO 2 at 1500 K and 3000 K. At these temperatures, the system seems to be made of slightly distorted GeO 4 tetrahedra which are linked by corners and have a Ge − O − Ge angle of 130 o , similar to the experimental value in the amorphous phase (GeO 2 glass). A volume collapse, in the range 4 − 8 GP a, is seen from the pressure-volume curve and may be the signature of a liquid-liquid phase transition, in analogy with water [120]. Van Hoang has carried out a similar study [59] factor T (r) compared to experimental findings [57].…”

Thermodynamic and Structural Characterization of the Transformation from a Metastable Low‐Density to a Very High‐Density Form of Supercooled TIP4P‐Ew Model Water

“…[10] Simulation studies suggest that VHDA ice should be considered as the amorphous solid counterpart to the high-density liquid water phase under ambient conditions, rather than HDA. [11,12] Koza et al [13] demonstrated, by using inelastic neutron scattering, that HDA and VHDA ice appear to be heterogeneous on the length scale of nanometers, and that different forms of HDA ice are obtained, depending on the exact preparation process. [13] By annealing HDA ice at normal pressure Tulk et al [14] observed a multitude of (metastable) amorphous ice states.…”