Incorporating QM/MM Molecular Dynamics Into the Few‐Mode Quantization Approach for Light–Matter Interactions in Nanophotonic Structures

ABSTRACT In the context of light–matter interactions between organic chromophores and confined photons of (plasmonic) nano‐resonators, we introduce a general framework that couples ab‐initio quantum mechanics/molecular mechanics (QM/MM) molecular dynamics with a recent quantization approach that allows to describe the electromagnetic field in nanophotonic environments with just a few modes. Arbitrary, lossy, and spatially inhomogeneous photonic environments are represented by a minimal set of interacting photonic modes fitted to the spectral density of the light‐confining structure, while geometry‐dependent molecular properties are computed on the fly. Applications to few‐molecule strong coupling show that strong light–matter interactions persist when molecular degrees of freedom and disorder are included for the chosen system consisting of a nanoparticle dimer coupled to five emitters. At the same time, symmetry‐protected degeneracies when modeling these five emitters as two‐level‐systems are lifted. The framework further reveals how spatial field inhomogeneity and molecular disorder shape cavity‐mediated energy transfer. This is illustrated for a donor–acceptor pair consisting in a photo‐reactive molecule that becomes resonant to the acceptor upon a light‐induced intramolecular proton transfer reaction.