Liquid water has anomalous liquid properties, such as its density maximum at 4 °C. An attempt at theoretical explanation proposes a liquid-liquid phase transition line in the supercooled liquid state, with coexisting low-density liquid (LDL) and high-density liquid (HDL) states. This line terminates at a critical point. It is assumed that the LDL state possesses mesoscopic tetrahedral structures that give it solidlike properties, while the HDL is a regular random liquid. But the short-lived nature of these solidlike structures makes them difficult to detect directly. We take a thermodynamic approach instead and calculate the thermodynamic Ricci curvature scalar R in the metastable liquid regime. It is believed that solidlike structures signal their presence thermodynamically by a positive sign for R, with a negative sign typically present in less organized fluid states. Using thermodynamic data from ST2 computer simulations fit to a mean field (MF) two state equation of state, we find significant regimes of positive R in the LDL state, supporting the proposal of solidlike structures in liquid water. In addition, we review the theory, compute critical exponents, demonstrate the large reach of the MF critical regime, and calculate the Widom line using R.
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14 August 2019
Research Article|
August 08 2019
Thermodynamic metric geometry of the two-state ST2 model for supercooled water
Special Collection:
Chemical Physics of Supercooled Water
Peter Mausbach
;
Peter Mausbach
a)
1
Technical University of Cologne
, Cologne, Germany
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Helge-Otmar May;
Helge-Otmar May
b)
2
University of Applied Sciences
, Darmstadt, Germany
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George Ruppeiner
George Ruppeiner
3
New College of Florida
, Sarasota, Florida 34243, USA
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b)
Deceased.
Note: This paper is part of a JCP Special Topic on Chemical Physics of Supercooled Water.
J. Chem. Phys. 151, 064503 (2019)
Article history
Received:
April 23 2019
Accepted:
July 16 2019
Citation
Peter Mausbach, Helge-Otmar May, George Ruppeiner; Thermodynamic metric geometry of the two-state ST2 model for supercooled water. J. Chem. Phys. 14 August 2019; 151 (6): 064503. https://doi.org/10.1063/1.5101075
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