title: Two-state thermodynamics of the ST2 model for supercooled water.
abstract: Thermodynamic properties of the ST2 model for supercooled liquid water exhibit anomalies similar to those observed in real water. A possible explanation of these anomalies is the existence of a metastable, liquid-liquid transition terminated by a critical point. This phenomenon, whose possible existence in real water is the subject of much current experimental work, has been unambiguously demonstrated for this particular model by most recent simulations. In this work, we reproduce the anomalies of two versions of the ST2 model with an equation of state describing water as a non-ideal "mixture" of two different types of local molecular order. We show that the liquid-liquid transition in the ST2 water is energy-driven. This is in contrast to another popular model, mW, in which non-ideality in mixing of two alternative local molecular orders is entropy-driven, and is not sufficiently strong to induce a liquid-liquid transition.
authors.affiliation: Institute for Physical Science and Technology and Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Vincent
authors.initials: V
authors.lastname: Holten
authors.affiliation: Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Jeremy C
authors.initials: JC
authors.lastname: Palmer
authors.affiliation: Department of Physics, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada.
authors.forename: Peter H
authors.initials: PH
authors.lastname: Poole
authors.affiliation: Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Pablo G
authors.initials: PG
authors.lastname: Debenedetti
authors.affiliation: Institute for 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