Data-Driven Many-Body Models for Molecular Simulations of Ions in Water: From Ionic Clusters to Concentrated Electrolyte Solutions

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Dr. Francesco Paesani of the University of California-San Diego is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry. A quantitative, molecular-level characterization of the structural, thermodynamic, dynamical, and spectroscopic properties of ions in aqueous environments under different conditions is key to understanding several fundamental processes, including ion-molecule reactions and ion-induced nucleation in the atmosphere, acid-base reactions in solution, ion transport in biological channels, and multiphase processes at air/liquid and solid/liquid interfaces. A unified picture of the behavior of hydrated ions across different phases and in different environments is particularly challenging, requiring a quantitative assessment of competing enthalpic and entropic effects associated with the interplay between ion–ion, ion–water, and water–water interactions, which are further modulated by nuclear quantum effects. By combining data-driven many-body potential energy functions derived entirely from high-level ab initio reference data with both classical and quantum molecular dynamics, Paesani will extend his many-body molecular dynamics (MB-MD) methodology to the modeling of ions in water, from gas-phase clusters to bulk solutions. The MB-MD methodology provides an accurate, yet efficient, theoretical/computational framework for molecular simulations of aqueous systems with high accuracy and predictive power. In this research project Paesani aims to develop a microscopic understanding of single-ion hydration structure and thermodynamics from small gas-phase clusters to bulk solutions in terms of individual many-body contributions, determine single-ion hydration free energies and ion–ion association free energies and decompose them in terms of elementary ion–water and water–water many-body effects, and characterize water hydrogen-bond structure and dynamics in electrolyte solutions as a function of ion concentration and composition, disentangling ion–ion, ion–water and water–water contributions. The theoretical/ computational methodology developed as part of the proposed research will have broad impact on a wide range of user communities from chemistry to materials science and biology, and will involve the training and education of high school, undergraduate and graduate students who will acquire a solid foundation in theoretical, computational, and physical chemistry. The interdisciplinary nature of the proposed project will provide the students with the opportunity to work at the interface of different disciplines which will prepare them for a wide range of careers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.