Cavity Quantum Electrodynamics Complete Active Space Configuration Interaction Theory

Abstract

Polariton chemistry has attracted great attention as a potential route to modify chemical structure, properties, and reactivity through strong interactions among molecular electronic, vibrational, or rovibrational degrees of freedom. A rigorous theoretical treatment of molecular polaritons requires the treatment of matter and photon degrees of freedom on equal quantum mechanical footing. In the limit of molecular electronic strong or ultrastrong coupling to one or a few molecules, it is desirable to treat the molecular electronic degrees of freedom using the tools of ab initio quantum chemistry, yielding an approach we refer to as ab initio cavity quantum electrodynamics, where the photon degrees of freedom are treated at the level of cavity quantum electrodynamics. Here, we present an approach called Cavity Quantum Electrodynamics Complete Active Space Configuration Interaction theory to provide ground-and excited-state polaritonic surfaces with a balanced description of strong correlation effects among electronic and photonic degrees of freedom. This method provides a platform for ab initio cavity quantum electrodynamics when both strong electron correlation and strong light−matter coupling are important and is an important step toward computational approaches that yield multiple polaritonic potential energy surfaces and couplings that can be leveraged for ab initio molecular dynamics simulations of polariton chemistry.

Cavity Quantum Electrodynamics Enables para- and ortho-Selective Electrophilic Bromination of Nitrobenzene

“…In addition, for this case cavity modified ground-state chemistry does not require the usual resonance effects of light–matter interactions (i.e., frequency matching between light and matter excitations) since the cavity can directly modify how the ground state of the hybrid system couples to the molecular system through the cavity mode’s vacuum fluctuations, referred to as quantum vacuum fluctuation modified chemistry. , Importantly, predictions based on single molecules coupled to a cavity are also within the reach of the magnitude of the strong coupling shown in recent experiments using a plasmonic nanocavity . A conceptual understanding of these recently proposed ground-state modifications due to cavity vacuum fluctuations ,,,,− is provided in the Theoretical Methods section. From an experimental perspective, cavity vacuum fluctuations have already been shown to modify the work function of materials inside the cavity, as predicted by early theory work …”

“… 15 , 21 Importantly, predictions based on single molecules coupled to a cavity are also within the reach of the magnitude of the strong coupling shown in recent experiments using a plasmonic nanocavity. 24 A conceptual understanding of these recently proposed ground-state modifications due to cavity vacuum fluctuations 9 , 15 , 17 , 21 , 25 − 27 is provided in the Theoretical Methods section. From an experimental perspective, cavity vacuum fluctuations have already been shown to modify the work function of materials inside the cavity, 28 as predicted by early theory work.…”

Comparing parameterized and self-consistent approaches to ab initio cavity quantum electrodynamics for electronic strong coupling

“…QED-Hartree-Fock, QED-CC, QED-CASCI) has been performed after transforming Eq. 1 to the coherent-state basis 36,40,47,48 ,…”

“…where |Φ I ⟩ represents an electronic Slater determinant, |n⟩ is a photon-number state corresponding to n photons in the cavity mode, and C I,n is an expansion coefficient 40 . Then, a variational scQED approach can be formulated as a matrix diagonalization problem where Eq.…”

“…In the limit of molecular electronic strong or ultra-strong coupling to one or a few molecules, it is desirable to treat the molecular electronic degrees of freedom using the tools of ab initio quantum chemistry, yielding an approach referred to as ab initio cavity quantum electrodynamics (ai-QED), where the photon degrees of freedom are treated at the level of cavity quantum electrodynamics. Two complementary approaches have emerged for ai-QED: (1) parameterized CQED 20,[23][24][25][26][27] (pQED), a twostep approach where the matter degrees of freedom are computed using existing electronic structure theories, enabling one to build rigorous ai-QED Hamiltonians in a basis of many-electron eigenstates, and (2) self-consistent CQED 19,[28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] (scQED), a one-step approach where electronic structure methods are generalized to include coupling between electrons and photon degrees of freedom.…”