Quasi-harmonic approximation of thermodynamic properties of ice Ih, II, and III

TL;DR

This study applies a quasi-harmonic approximation to analyze thermodynamic properties of ice Ih, II, and III, offering a computationally efficient method that captures quantum effects and aligns well with more intensive simulation results.

Contribution

It demonstrates the effectiveness of the quasi-harmonic approximation in predicting thermodynamic properties of ice phases with reduced computational cost.

Findings

Accurately reproduces quantum and classical simulation results at low temperatures

Maintains good agreement across a range of pressures away from mechanical stability limits

Provides insights into quantum effects on ice thermodynamics

Abstract

Several thermodynamic properties of ice Ih, II, and III are studied by a quasi-harmonic approximation and compared to results of quantum path integral and classical simulations. This approximation allows to obtain thermodynamic information at a fraction of the computational cost of standard simulation methods, and at the same time permits studying quantum effects related to zero point vibrations of the atoms. Specifically we have studied the crystal volume, bulk modulus, kinetic energy, enthalpy and heat capacity of the three ice phases as a function of temperature and pressure. The flexible q-TIP4P/F model of water was employed for this study, although the results concerning the capability of the quasi-harmonic approximation are expected to be valid independently of the employed water model. The quasi-harmonic approximation reproduces with reasonable accuracy the results of quantum and classical simulations showing an improved agreement at low temperatures (T < 100 K). This agreement does not deteriorate as a function of pressure as long as it is not too close to the limit of mechanical stability of the ice phases.