Molecular systems strongly coupled to an optical cavity with nanoconfined photons exhibit some interesting chemical and physical properties, e.g., changes in photochemical reactions and catalysis, existence of polariton states (strong interactions between photons and molecular electric dipole moments), and even superfluidity at room temperature. <i>Ab initio</i> formulations of cavity quantum electrodynamics (cQED) methods have become increasingly effective in recent years for studying the light-matter interactions of molecules confined in small optical cavities. So far, the electronic structure properties of molecular systems trapped in small cavities have been examined using the cQED formalism with Hamiltonians in conjunction with density functional theory (cQED-DFT), Hartree-Fock theory (cQED-HF), and the more sophisticated coupled-cluster theory (cQED-CC). We evaluate the performance of a new <i>ab initio</i> approach: the cQED variational two-electron reduced-density matrix (cQED-v2RDM) method. This method provides a polynomial scaling description of strong and nondynamic correlation effects in molecular systems. We use the cQED-v2RDM method to explore the electronic structure properties of oligoacene molecules in a cavity. Specifically, we investigate how the presence of the cavity affects the singlet-triplet energy gap as a function of the cavity coupling strength and the cavity frequency. Moreover, we analyze how the cavity changes the possible polyradical character and delocalized nature of the singlet state. Therefore, this study brings us one step closer to achieving a better understanding of the unusual electronic structure properties that can emerge in oligoacene molecules embedded in a small optical cavity.

Understanding the electronic structure properties of oligoacene molecules in small optical cavities

ACS Spring 2022

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