Density Functional Atom-In-Molecule Force Field for Charge Transfer Systems*

Given an arbitrary molecular structure and corresponding total electronic density, the Hohenberg-Kohn theorem of density functional theory induces an approximate but unique atom-in-molecule density decomposition [1]. The decomposition is expressed as an ensemble-of-ensembles, a weighted double sum over ionic and excited state densities, and yields effective atomic charges consistent with chemical intuition, and in remarkable accord with the topological AIM theory of Bader. We show that this decomposition further induces a corresponding ensemble energy expression and multiscale force field appropriate for open, charge-transfer dynamical systems simulation. [1] SR Atlas, J Dittman, V Janardhanam, G Amo-Kwao, and SM Valone, to be submitted (2013).