Herein we present a methodology for developing accurate and transferable water force fields based on advanced ab initio theories. Historically, explicit water force fields have been designed as `effective potentials': models which combine multiple physical effects into a single functional form intended to effectively (if only very approximately) capture the relevant physics of intermolecular interactions. By fitting the parameters of these effective potentials to experimental data, a subset of water properties can thus be captured with great accuracy. However, due to the approximate nature of these potentials, most simple water models lack transferability, and are thus not able to accurately predict water properties in physical and/or chemical environments significantly different from the experimental conditions used during force field parameterization.<br/><br/>Rather than create effective pair potentials, here we present a strategy for developing ab initio water force fields based on 1) a physically-inspired description of the molecular electron density and 2) a term-by-term parameterization strategy which separately accounts for the various sources (electrostatic, exchange, induction, and dispersion) of intermolecular interactions. Crucially, our newly-developed `MASTIFF' methodology allows us to account for the atomic-level anisotropy of water's electron density, not only in the electrostatic term (as do several recent water models), but also in the exchange, induction, and dispersion terms. The accuracy and transferability of the MASTIFF model will be discussed in comparison to both theoretical and experimental benchmarks, thus highlighting its modest computational cost, broad applicability to simulations of both simple liquids and mixtures, and enhanced transferability in a variety of chemical and physical environments.

<i>Ab initio</i> force fields for water: The multifaceted roles of atomic charge density anisotropy

2019 Spring National Meeting

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Ab initio force fields for water: The multifaceted roles of atomic charge density anisotropy