Transferable Ion Force Fields in Water from a Simultaneous Optimization of Ion Solvation and Ion-Ion Interaction.

Philip Loche,Roland R Netz,Douwe Jan Bonthuis,Sean Friedowitz,Patrick Steinbrunner

doi:10.1021/acs.jpcb.1c05303

Philip Loche, Roland R Netz + Show 3 more

Open Access

https://doi.org/10.1021/acs.jpcb.1c05303

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Abstract

The poor performance of many existing nonpolarizable ion force fields is typically blamed on either the lack of explicit polarizability, the absence of charge transfer, or the use of unreduced Coulomb interactions. However, this analysis disregards the large and mostly unexplored parameter range offered by the Lennard-Jones potential. We use a global optimization procedure to develop water-model-transferable force fields for the ions K+, Na+, Cl–, and Br– in the complete parameter space of all Lennard-Jones interactions using standard mixing rules. No extra-thermodynamic assumption is necessary for the simultaneous optimization of the four ion pairs. After an optimization with respect to the experimental solvation free energy and activity, the force fields reproduce the concentration-dependent density, ionic conductivity, and dielectric constant with high accuracy. The force field is fully transferable between simple point charge/extended and transferable intermolecular potential water models. Our results show that a thermodynamically consistent force field for these ions needs only Lennard-Jones and standard Coulomb interactions.

Highlights

Aqueous electrolyte solutions play an important role for all living organisms and have wide electrochemical applications with many economical and environmental advantages compared to nonaqueous solvents.[1]
Used nonpolarizable ion force fields include those by Smith,[2,3] Dang,[4] and the Groningen Molecular Simulation (GROMOS) set[5] for the simple point charge/extended (SPC/E) water model and the Assisted Model Building with Energy Refinement (AMBER),[6] the Chemistry at Harvard Macromolecular Mechanics (CHARMM),[7] and optimized versions based on these[8] for the transferable intermolecular potential (TIP) water model family
We introduce a classical nonpolarizable force field for K+, Na+, Cl− and Br− optimized for the SPC/E water model, the parameters of which are directly transferable to other major water models, in particular, TIP3P, TIP4P/ε, and, to a lesser degree of accuracy, TIP4P

Summary

Introduction

Aqueous electrolyte solutions play an important role for all living organisms and have wide electrochemical applications with many economical and environmental advantages compared to nonaqueous solvents.[1]. Used nonpolarizable ion force fields include those by Smith,[2,3] Dang,[4] and the Groningen Molecular Simulation (GROMOS) set[5] for the simple point charge/extended (SPC/E) water model and the Assisted Model Building with Energy Refinement (AMBER),[6] the Chemistry at Harvard Macromolecular Mechanics (CHARMM),[7] and optimized versions based on these[8] for the transferable intermolecular potential (TIP) water model family. These force fields produce conflicting results for a number of important systems, including DNA9,10 and lipid membranes,[11] and must be amended for proteins.[12]

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