title: Two-structure thermodynamics for the TIP4P/2005 model of water covering supercooled and deeply stretched regions.
abstract: One of the most promising frameworks for understanding the anomalies of cold and supercooled water postulates the existence of two competing, interconvertible local structures. If the non-ideality in the Gibbs energy of mixing overcomes the ideal entropy of mixing of these two structures, a liquid-liquid phase transition, terminated at a liquid-liquid critical point, is predicted. Various versions of the "two-structure equation of state" (TSEOS) based on this concept have shown remarkable agreement with both experimental data for metastable, deeply supercooled water and simulations of molecular water models. However, existing TSEOSs were not designed to describe the negative pressure region and do not account for the stability limit of the liquid state with respect to the vapor. While experimental data on supercooled water at negative pressures may shed additional light on the source of the anomalies of water, such data are very limited. To fill this gap, we have analyzed simulation results for TIP4P/2005, one of the most accurate classical water models available. We have used recently published simulation data, and performed additional simulations, over a broad range of positive and negative pressures, from ambient temperature to deeply supercooled conditions. We show that, by explicitly incorporating the liquid-vapor spinodal into a TSEOS, we are able to match the simulation data for TIP4P/2005 with remarkable accuracy. In particular, this equation of state quantitatively reproduces the lines of extrema in density, isothermal compressibility, and isobaric heat capacity. Contrary to an explanation of the thermodynamic anomalies of water based on a "retracing spinodal," the liquid-vapor spinodal in the present TSEOS continues monotonically to lower pressures upon cooling, influencing but not giving rise to density extrema and other thermodynamic anomalies.
authors.affiliation: Institute of Physical Science and Technology and Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: John W
authors.initials: JW
authors.lastname: Biddle
authors.affiliation: Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Rakesh S
authors.initials: RS
authors.lastname: Singh
authors.affiliation: Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Evan M
authors.initials: EM
authors.lastname: Sparano
authors.affiliation: Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Francesco
authors.initials: F
authors.lastname: Ricci
authors.affiliation: Departamento Química Física I, Facultad Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain.
authors.forename: Miguel A
authors.identifier: 0000000164195263
authors.initials: MA
authors.lastname: González
authors.affiliation: Departamento Química Física I, Facultad Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain.
authors.forename: Chantal
authors.identifier: 0000000205024648
authors.initials: C
authors.lastname: Valeriani
authors.affiliation: Departamento Química Física I, Facultad Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain.
authors.forename: José L F
authors.identifier: 0000000203043407
authors.initials: JL
authors.lastname: Abascal
authors.affiliation: Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Pablo G
authors.identifier: 0000000318811728
authors.initials: PG
authors.lastname: Debenedetti
authors.affiliation: Institute of Physical Science and Technology and Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Mikhail A
authors.initials: MA
authors.lastname: Anisimov
authors.affiliation: Univ Lyon, Université Claude Bernard Lyon 1, CNRS, Institut Lumière Matière, F-69622 Villeurbanne, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Caupin