Atomwise force fields for molten alkali chlorides (LiCl and KCl) and their mixtures: efficient parameterization via genetic algorithms

Over the last few decades, molten salts have gained significant attention in the field of green energy pro-duction. One useful method that can accelerate the discovery and optimization of desirable molten salts from a vast range of materials is classical molecular dynamics (CMD). However, because of the absence of CMD force fields that can reasonably reproduce experimental physical properties, the use of CMD to study molten salts remains a significant challenge. Hence, in this study, we report non-polarizable rigid ion models (RIMs) for the widely used LiCl, KCl, and LiCl-KCl molten salts, obtained via genetic algo-rithms (GAs). Based on the results presented in this study, GAs proved to be very effective in simultane-ously optimizing a large number of force field parameters. With GAs, the force field generation process is automated and no manual intervention is required. The RIM force fields developed herein can reason-ably reproduce experimental physical properties at different temperatures and various salt compositions, provides microstructural characteristics similar to those obtained using highly accurate and reliable first -principles MD, and an improved overall performance in contrast to previously reported polarizable force fields, all at a lower computational cost. In contrast to previous studies, we developed atomwise RIM force fields that employ mixing rules for interactions between ions of different types. This reduced the total number of optimizable terms, and thus resulted in RIM parameters that are transferrable between different molten salt systems.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

In the field of green energy production, molten salts have gained significant attention over the last few decades. Classical molecular dynamics (CMD) is a useful method for discovering and optimizing desirable molten salts, but the absence of CMD force fields that can accurately reproduce experimental physical properties poses a challenge. In this study, non-polarizable rigid ion models (RIMs) for widely used LiCl, KCl, and LiCl-KCl molten salts were developed using genetic algorithms (GAs). The results show that GAs are effective in optimizing force field parameters and the developed RIM force fields can reasonably reproduce experimental physical properties, providing microstructural characteristics similar to first-principles MD and improved overall performance at a lower computational cost. The developed atomwise RIM force fields with mixing rules for interactions between ions of different types reduce the total number of optimizable terms and enable transferability between different molten salt systems.