Thermochemical properties of anhydrous crystals and molten alkali metal halide salts from molecular simulations of phase-transferable polarizable force fields

Abstract

Alkali halides find application not only under standard thermodynamic conditions but also at elevated temperatures, for example, in molten salt reactors or heat transfer and storage in solar applications. This study presents the temperature dependence of the thermochemical properties of their salts at normal pressure and temperatures ranging from 298.15 K up to the boiling points of the salts. The values were obtained using molecular simulations with polarizable DLM/2022-BK3 force fields. In most cases, our results show excellent agreement with experiments and often similar or better predictive capability compared to the most accurate polarizable models available in the literature developed for simulations of anhydrous alkali halides. Relatively worse predictions are observed for salts in which very small anions strongly polarize large cations. Our results for density, energy, chemical potential, and heat capacity of melts and crystals, and also melting temperatures, confirm the excellent phase transferability of the force fields used. They also serve as a substitute for missing experimental data for rubidium and cesium halides and highlight inaccuracies in some experimental data for the densities of LiBr, NaF, and NaBr crystals found in the literature.