Cavity-modified electronic interactions in molecular ensembles under vibrational strong coupling: Combined insights from cavity Born-Oppenheimer perturbation and ab initio wave function theories

TL;DR

This paper develops a theoretical framework combining cavity Born-Oppenheimer perturbation and wave function theories to analyze how vibrational strong coupling modifies electronic interactions in molecular ensembles, revealing subtle energy corrections and long-range effects.

Contribution

It introduces a combined perturbative and non-perturbative approach to study cavity-induced electronic interaction modifications in molecules under vibrational strong coupling.

Findings

Small local modifications of molecular potential energy surfaces.

Excellent agreement between perturbative and wave function methods.

Enhanced long-range intermolecular interactions under cavity influence.

Abstract

Resonant vibrational strong coupling (VSC) between molecular vibrations and quantized field modes of low-frequency optical cavities constitutes the conceptual cornerstone of vibro-polaritonic chemistry. In this work, we theoretically investigate complementary nonresonant electron-cavity mode-interactions in the cavity Born-Oppenheimer (CBO) approximation. We focus on cavity-induced modifications of local and non-local electronic interactions in dipole-coupled molecular ensembles under VSC. Methodologically, we combine CBO perturbation theory (CBO-PT) [Fischer, Saalfrank, JCTC 19, 7215 (2023)] with non-perturbative CBO Hartree-Fock and coupled cluster theories. Wave function approaches are reformulated to self-consistently address a cavity reaction potential (CRP), which minimizes the electronic energy in the cavity subspace. We derive up to second-order CBO-PT corrections of intra- and intermolecular energies revealing non-trivial corrections to dipole-dipole, dipole-induced-dipole and van-der-Waals interactions, and provide analytical second-order CRP for unimolecular and interacting bimolecular scenarios. In the unimolecular case, we find small local modifications of molecular PES for selected isomerization reactions dominantly captured by the first-order dipole fluctuation. Excellent agreement between CBO-PT and non-perturbative wave function results is obtained indicating minor VSC-induced state relaxation effects in the single-molecule limit. In the bimolecular scenario, CBO-PT reveals an explicit coupling of interacting dimers to cavity modes besides cavity-polarization dependent dipole-induced-dipole and van-der-Waals interactions with enhanced long-range character. An illustrative CBO-CCSD-based numerical analysis of selected molecular dimer models provides a complementary non-perturbative perspective on cavity-modified intermolecular interactions under VSC.