Modification of micro- and macroproperties of plasmon-molecule systems by strong coupling

Plasmonic-molecular systems are gaining interest as a platform to studying strong light-matter coupling effects, owing to small mode volumes of plasmonic modes and relatively small systems sizes (hundreds of atoms) enabling tackling them by the ab initio methods. In our work we use real-time TD-DFT method to study what modifications of the systems occur under strong coupling conditions, including plasmon redshift and molecular absorption quenching. We observe mixed transitions, i.e. ocurring when the initial and excited states are located in different subparts of the system, as well as the drastic modifications of the molecular oscillator when modeling the systems with the coupled oscillators model. We show how atomistic scale effects influence the coupling and how to tailor the polaritonic states to obtain desired features in the system.