Many-Body Second Order Green's Function Theory for Ab Initio Molecular Quantum Electrodynamics
Abstract
In this work, we develop two many-body quantum electrodynamic methods to calculate the ground-state energies of strongly coupled light-matter molecular systems. Specifically, we extend the second-order many-body Green's function theory (GF2) for electronic systems to incorporate electron-boson couplings. We employ two ansätze to treat the bosonic part of the system, namely the coherent-state (CS) and Lang-Firsov (LF) transformed vacuum state. These are combined with the GF2 method to construct two new approaches, which we refer to as CS-GF2 and LF-GF2. We benchmark CS- and LF-GF2 by studying various molecular systems inside an optical cavity. We investigate H2 and LiH potential energy surfaces, keto-eneol tautomerization energy barrier, van-der Waals interactions between two H2 molecules and the torsional potential energy surface of the ethylene molecule, C2H4. Both methods provide highly accurate energies, with only modest additional improvement observed in LF-GF2.
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