Non-Hermitian Cavity Quantum Electrodynamics - Configuration Interaction Singles Approach for Polaritonic Structure with ab initio Molecular Hamiltonians

We combine {ab initio molecular electronic Hamiltonians with a cavity quantum electrodynamics model for dissipative photonic modes and apply mean-field theories to the ground- and excited-states of resulting polaritonic systems. In particular, we develop a restricted Hartree-Fock theory for the mean-field ground-state and a non-Hermitian configuration interaction singles theory for mean-field excited-states of the molecular system strongly interacting with a photonic mode, and apply these methods to several paradigmatic polaritonic systems. We leverage the Psi4Numpy framework to yield open-source and accessible reference implementations of these methods.