Cavity Quantum Electrodynamics Ring Coupled Cluster and the Random Phase Approximation

TL;DR

This paper extends the equivalence between RPA and ring-CCD models from traditional quantum chemistry to cavity QED, showing their numerical equivalence in this new context.

Contribution

It generalizes the known RPA and ring-CCD equivalence to cavity QED systems, including photon interactions.

Findings

QED-RPA and QED ring-CCD are numerically equivalent.

The generalized model includes double electron and photon excitations.

The approach accounts for coupled electron and photon creation processes.

Abstract

It is well known that the ground-state correlation energy from the particle-hole channel of the random phase approximation (RPA) is formally equivalent to that from a simplified coupled cluster doubles (CCD) model that includes only ring diagram contraction contributions in the residual equations [{\em J. Chem. Phys.} {\bf 129}, 231101 (2008)]. We generalize this analytic result to the cavity quantum electrodynamics (QED) case and demonstrate the numerical equivalence of QED-RPA and a QED ring-CCD model that accounts for double electron excitations, coupled single electron excitations / single photon creation, and double photon creation.