Molecular dynamics (MD) simulations have become an invaluable tool, allowing for a detailed investigation of chemical phenomena that are experimentally inaccessible. While there are many approaches one may take to model the relevant intermolecular interactions, such as density functional theory (DFT), or simple force fields, many of these methods cannot offer a sufficient balance of accuracy and cost for condensed phase systems. In this context, the use of analytical potential energy functions (PEFs) derived from the many-body expansion of the interaction energy for a given system is one of the more promising approaches for representing intermolecular interactions. The MB-nrg PEFs for halide-water interactions are able to reproduce CCSD(T)-F12b energies (extrapolated to the complete basis set limit) at a fraction of the cost of any DFT model. These PEFs consist of classical representations of permanent electrostatics (ELEC), polarization (POL), and London dispersion (DISP) energies, which reproduce interaction energies at large intermolecular separations, supplemented with data-driven close-range potentials, expressed in terms of permutationally invariant polynomials (PIPs) for two-body (2B) and three-body (3B) interaction energies. The PIPs can be seen as "quantum corrections" to the underlying long-range potential, effectively recovering non-classical interactions such as charge transfer (CT) and Pauli repulsion (PAULI), in addition to correcting deficiencies of the classical electrostatics, such as charge penetration (CP). Using the absolutely localized molecular orbital energy decomposition analysis (ALMO EDA), which decomposes DFT interaction energies into terms such as PAULI, ELEC, DISP, POL, and CT, we demonstrate that in spite of lacking explicit representations of effects such as CT and CP, the MB-nrg PIPs provide an implicit representation of all relevant interactions. In order to emphasize the fact that MB-nrg does not work by accident, we compare its energy decompositions to those calculated with two sets of simple classical PEFs, and various DFT models.

MB-nrg doesn't work by accident!

2019 Fall National Meeting

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