2025 AIChE Annual Meeting

(389aq) Improving the Force Field Performance of Ionic Species within the Openff Workflow

Authors

Michael Shirts, University of Colorado Boulder
This research presents our developing methodology for validating and optimizing ion force field parameters within the Open Force Field initiative. The accuracy of ion parameters in fixed-charge force fields is highly sensitive to the broader force field context, including water models. Our proposed workflow is designed to produce transferable force field parameters—initially for alkali, alkali earth, and halide ions, but extending to polyatomic anions, that accurately model ion-dipole, van der Waals, electrostatic, and hydrogen-bonding interactions across diverse chemical environments.

To improve agreement with experimental data, we employ underutilized validation metrics such as osmotic coefficients and examine both monoatomic and organic polyatomic ions in non-polarizable force fields, balancing computational efficiency with predictive accuracy. We compare two computational approaches for calculating osmotic coefficients—the flat-bottom potential method and the harmonic potential method—highlighting their respective analyses.

Our assessment explores the limitations of non-polarizable force field models, identifying their constraints and determining when alternative functional forms or advanced theories, such as polarizability, become necessary. Ultimately, our methodology aims to enhance the applicability of simulations involving complex ionic interactions and establish a rigorous workflow for electrolyte force field development in molecular dynamics.