We present the ongoing development of numerically efficient potential energy functions (PEFs) for molecular-ion–water systems based upon the many-body expansion of the interaction energy.  These highly-accurate and stable PEFs are fully compatible with the previously reported and well-established MB-pol potential for water and the broader MB-nrg family of PEFs, and represent the first extension of the MB-nrg family to describing molecular-ion–water interactions.  Dominating the short-range portion of the PEFs are permutationally invariant polynomials which have been fit to reproduce ab initio electronic structure data, thereby capturing the quantum mechanical interactions arising from the overlap of electron densities.  This short-range portion transitions smoothly into a long-range portion consisting of classical expressions for electrostatic, dispersion, and many-body induction interactions.  The accuracy and stability of the explicit one- and two-body terms of the PEFs are assessed with respect to the reference DFT data based on a number of energetic and structural features/criteria.  Comparison with analogous classical polarizable force fields developed alongside these MB-nrg PEFs demonstrates the need for a complex functional form capable of capturing the short-range, quantum mechanical behavior in obtaining a realistic and reliable molecular-level description of molecular-ion–water systems.  Important considerations regarding training set generation (sampling), fitting, and representation will also be discussed.<br/>

Development of accurate potential energy functions for molecular-ion–water interactions through the many-body expansion

2019 Fall National Meeting

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