Phase diagram of the ST2 model of water

TL;DR

This paper maps the phase diagram of the ST2 water model, identifying phase boundaries, critical points, and the relation between liquid-liquid criticality and crystalline phases, aiding understanding of water's complex behavior.

Contribution

It provides the first detailed free energy calculations and phase boundary estimates for the ST2 water model with reaction field corrections.

Findings

Identified the phase coexistence boundaries in the temperature-pressure plane.

Located the gas-liquid critical point and coexistence conditions.

Framed the liquid-liquid critical point relative to crystalline phases.

Abstract

We evaluate the free energy of the fluid and crystal phases for the ST2 potential [F.H. Stillinger and A. Rahman, J. Chem. Phys. 60, 1545 (1974)] with reaction field corrections for the long-range interactions. We estimate the phase coexistence boundaries in the temperature-pressure plane, as well as the gas-liquid critical point and gas-liquid coexistence conditions. Our study frames the location of the previously identified liquid-liquid critical point relative to the crystalline phase boundaries, and opens the way for exploring crystal nucleation in a model where the metastable liquid-liquid critical point is computationally accessible.