We have developed a variational formulation of the electrostatically-embedded generalized many-body expansion, in which a system's energy is written in terms of subsystem energies consisting of monomers, dimers, trimers, … of fragments, but where those fragments are allowed to overlap, i.e., to share atoms in common. These subsystem calculations are computed in the electrostatic potential generated by point charges that come from the other fragments, in order to accelerate convergence of the expansion. Importantly, we do this in a manner that guarantees that the method is variational, even when the embedding charges are updated self-consistently. This greatly simplifies the formulation of analytic energy gradients yet ensures that those gradients are exact (with no neglected response terms) but do not require the costly solution of coupled-perturbed equations. Applications will be presented involving energy-conserving ab initio molecular dynamics within a fragment-based formalism.

Electrostatically-embedded fragment method with simple (and correct!) analytic gradient

2019 Spring National Meeting

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