title: Thermodynamic and structural characterization of the transformation from a metastable low-density to a very high-density form of supercooled TIP4P-Ew model water.
abstract: We explore the phase diagram of the metastable TIP4P-Ew liquid model water from 360 K down to 150 K at densities ranging from 0.950 to 1.355 g cm(-3). In addition to the low-density/high-density (LDL/HDL) liquid-liquid transition, we observe a structural high-density/very high-density (HDL/VHDL) transformation for the lowest temperatures at 1.30 g cm(-3). The characteristics of the isobars and isotherms suggest the presence of a stepwise HDL/VHDL transition with first-order-like appearance. In addition, we also identify an apparent pretransition at 1.24 g cm(-3), which suggests that the experimentally detected LDA/VHDA transformation might evolve into a multiple-step process with different local structures representing local minima in the free-energy landscape. Such a scenario is supported by a pronounced correlation between the isothermal density dependence of the pressure, with a stepwise increase of the oxygen coordination number, due to the appearance of interstitial water molecules.
authors.affiliation: Physikalische Chemie, Fakultät Chemie, TU Dortmund, Otto-Hahn-Str. 6,D-44227 Dortmund, Germany.
authors.forename: Dietmar
authors.initials: D
authors.lastname: Paschek
authors.forename: Andreas
authors.initials: A
authors.lastname: Rüppert
authors.forename: Alfons
authors.initials: A
authors.lastname: Geiger