Cavity Quantum Electrodynamic Nuclear-Electronic Orbital Complete Active Space Configuration Interaction

Polaritons offer the possibility of modifying chemical properties through the strong coupling of molecules to photons confined in optical cavities. From a first-principles perspective, understanding how these strong light-matter interactions cause chemical changes requires quantum mechanical descriptions of electrons, nuclei, and photons. Herein, we develop the ab initio cavity quantum electrodynamic nuclear-electronic orbital complete active space configuration interaction (QED-NEO-CASCI) method, in which electrons, specified nuclei, and cavity photons are all treated quantum mechanically. Using this method, we are able to describe hydrogen tunneling under vibrational strong coupling and geometry changes in a hydrogen-bonded complex coupled to a cavity. Under vibronic strong coupling, we observe features in the polaritonic absorption spectrum that correspond to Raman active transitions outside a cavity. We also develop the real-time variant, denoted time-dependent configuration interaction (QED-NEO-TDCI). This method allows us to simulate nonadiabatic hydrogen tunneling dynamics and observe the real-time quantum mechanical transfer of energy between the molecule and cavity photons. These methods provide the ab initio foundation for studying correlated electronic-nuclear-photonic chemical physics.