Configurational entropy of hydrogen-disordered ice polymorphs

TL;DR

This study calculates the configurational entropy of various hydrogen-disordered ice polymorphs using thermodynamic integration and Monte Carlo simulations, revealing correlations with structural parameters and network properties.

Contribution

It introduces a precise thermodynamic integration method to compute the configurational entropy of multiple ice phases, linking entropy to structural and network characteristics.

Findings

Entropy varies among ice polymorphs, with ices VI and XII having the highest and lowest values.

A strong correlation exists between configurational entropy and the connective constant of ice networks.

The method is validated on a 2D lattice model for reliability.

Abstract

The configurational entropy of several H-disordered ice polymorphs is calculated by means of a thermodynamic integration along a path between a totally H-disordered state and one fulfilling the Bernal-Fowler ice rules. A Monte Carlo procedure based on a simple energy model is used, so that the employed thermodynamic path drives the system from high temperatures to the low-temperature limit. This method turns out to be precise enough to give reliable values for the configurational entropy of different ice phases in the thermodynamic limit (number of molecules N --> infinity). The precision of the method is checked for the ice model on a two-dimensional square lattice. Results for the configurational entropy are given for H-disordered arrangements on several polymorphs, including ices Ih, Ic, II, III, IV, V, VI, and XII. The highest and lowest entropy values correspond to ices VI and XII, respectively, with a difference of 3.3\% between them. The dependence of the entropy on the ice structures has been rationalized by comparing it with structural parameters of the various polymorphs, such as the mean ring size. A particularly good correlation has been found between the configurational entropy and the connective constant derived from self-avoiding walks on the ice networks.