Molecular Modeling of Water-in-Salt Electrolytes: A Comprehensive Analysis of Polarization Effects and Force Field Parameters in Molecular Dynamics Simulations

Accurate modeling of highly concentrated aqueous solutions,suchas water-in-salt (WiS) electrolytes in battery applications, requiresproper consideration of polarization contributions to atomic interactions.Within the force field molecular dynamics (MD) simulations, the atomicpolarization can be accounted for at various levels. Nonpolarizableforce fields implicitly account for polarization effects by incorporatingthem into their van der Waals interaction parameters. They can additionallymimic electron polarization within a mean-field approximation throughionic charge scaling. Alternatively, explicit polarization descriptionmethods, such as the Drude oscillator model, can be selectively appliedto either a subset of polarizable atoms or all polarizable atoms toenhance simulation accuracy. The trade-off between simulation accuracyand computational efficiency highlights the importance of determiningan optimal level of accounting for atomic polarization. In this study,we analyze different approaches to include polarization effects inMD simulations of WiS electrolytes, with an example of a Na-OTF solution.These approaches range from a nonpolarizable to a fully polarizableforce field. After careful examination of computational costs, simulationstability, and feasibility of controlling the electrolyte properties,we identify an efficient combination of force fields: the Drude polarizableforce field for salt ions and non-polarizable models for water. Thiscost-effective combination is sufficiently flexible to reproduce abroad range of electrolyte properties, while ensuring simulation stabilityover a relatively wide range of force field parameters. Furthermore,we conduct a thorough evaluation of the influence of various forcefield parameters on both the simulation results and technical requirements,with the aim of establishing a general framework for force field optimizationand facilitating parametrization of similar systems.

Automated summary

Accurate modeling of highly concentrated aqueous solutions, such as WiS electrolytes, requires proper consideration of polarization contributions. This study analyzes different approaches to include polarization effects in MD simulations and identifies an efficient combination of force fields for Na-OTF solution: a Drude polarizable force field for salt ions and non-polarizable models for water. This cost-effective combination ensures simulation stability and reproduces a broad range of electrolyte properties.