Thermodynamic anomalies in a lattice model of water

TL;DR

This paper models water's anomalous thermodynamic behaviors using a lattice model with tetrahedral symmetry, revealing phase transitions, density maxima, and a possible second critical point in supercooled water.

Contribution

It introduces a simplified lattice model capturing water's anomalies, including phase behavior and critical phenomena, without donor-acceptor bond distinction.

Findings

Model reproduces water-like density anomalies.

Evidence of a second critical point in supercooled regime.

Reentrant spinodal possible under certain parameters.

Abstract

We investigate a lattice-fluid model of water, defined on a three-dimensional body centered cubic lattice. Model molecules possess a tetrahedral symmetry, with four equivalent bonding arms, aiming to mimic the formation of hydrogen bonds. The model is similar to the one proposed by Roberts and Debenedetti [J. Chem. Phys. 105, 658 (1996)], simplified in that no distinction between bond "donors" and "acceptors" is imposed. Bond formation depends both on orientation and local density. In the ground state, we show that two different ordered (ice) phases are allowed. At finite temperature, we analyze homogeneous phases only, working out phase diagram, response functions, the temperature of maximum density locus, and the Kauzmann line. We make use of a generalized first order approximation on a tetrahedral cluster. In the liquid phase, the model exhibits several anomalous properties observed in real water. In the low temperature region (supercooled liquid), there are evidences of a second critical point and, for some range of parameter values, this scenario is compatible with the existence of a reentrant spinodal.