Eur. Phys. J. E (2015) 38: 39
https://doi.org/10.1140/epje/i2015-15039-x

Regular Article

Free energy of formation of small ice nuclei near the Widom line in simulations of supercooled water

¹ Department of Physics, St. Francis Xavier University, B2G 2W5, Antigonish, NS, Canada
² Department of Chemistry, University of Saskatchewan, 57N 5C9, Saskatoon, SK, Canada
³ Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John’s, A1B 3X7, Newfoundland, Canada
⁴ Dipartimento di Fisica, Università di Roma “La Sapienza”, Piazzale A. Moro 5, 00185, Roma, Italy

^* e-mail: ppoole@stfx.ca

Received: 13 January 2015
Revised: 9 March 2015
Accepted: 11 March 2015
Published online: 21 May 2015

Abstract

The ST2 interaction potential has been used in a large number of simulation studies to explore the possibility of a liquid-liquid phase transition (LLPT) in supercooled water. Using umbrella sampling Monte Carlo simulations of ST2 water, we evaluate the free energy of formation of small ice nuclei in the supercooled liquid in the vicinity of the Widom line, the region above the critical temperature of the LLPT where a number of thermodynamic anomalies occur. Our results show that in this region there is a substantial free-energy cost for the formation of small ice nuclei, demonstrating that the thermodynamic anomalies associated with the Widom line in ST2 water occur in a well-defined metastable liquid phase. On passing through the Widom line, we identify changes in the free energy to form small ice nuclei that illustrate how the thermodynamic anomalies associated with the LLPT may influence the ice nucleation process.