Investigating Molecular Exciton-Polaritons using Many-body Electronic Structure Theory with Cavity Quantum Electrodynamics

Polariton chemistry has emerged recently as a new way to control chemistry using the quantum light-matter interactions by coupling molecules with an optical cavity. Much of the recent theoretical work in understanding exciton-polaritons has stemmed from reformulating electronic structure software to include the interactions between photonic and molecular degrees of freedom. In this work, we present a conceptually simple framework to uncovering these phenomena utilizing already-made and heavily tested electronic structure packages for the complicated molecular Hamiltonian and simply combining this information into the popular Pauli-Fierz Hamiltonian to perform a second diagonalization to obtain the polaritonic properties. In this way, we can also easily compute various quantities useful for analysis of the polaritonic excited states, including the transition density matrix, real-space projected transition density, mixed electron-photon transition density, natural transition orbitals, and linear spectroscopy.