We present a new development in quantum mechanics/molecular mechanics (QM/MM) methods by replacing conventional MM models with data-driven many-body (MB) representations rigorously derived from high-level QM calculations. The new QM/MB-MM approach builds on top of mutually polarizable QM/MM schemes developed for polarizable force fields with inducible dipoles and uses data-driven representations based on permutationally invariant polynomials to effectively account for short-range quantum-mechanical contributions (e.g., exchange-repulsion and charge transfer and penetration) that, arising from the overlap of the electron densities, are difficult to describe by classical expressions adopted by conventional MM models. Using our many-body MB-pol and MB-DFT potential energy functions for water, which include explicit two-body and three-body terms fitted to reproduce the corresponding CCSD(T) and DFT two-body and three-body energies for water, we demonstrate that the new QM/MB-MM approach guarantees a smooth energy transition as molecules are transferred between QM and MM regions, without the need of a transition layer. By effectively elevating the accuracy of both the MM region and the QM/MM interface to that of the QM region, the new QM/MB-MM approach achieves an accuracy comparable to that obtained with a fully QM treatment of the entire system.

Explicit many-body, fully polarizable approach to QM/MM simulations

ACS Spring 2022

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