Strong Coupling between Localized Surface Plasmons and Molecules by Coupled Cluster Theory.

Jacopo Fregoni,Tommaso Giovannini,Stefano Corni,Silvio Pipolo,Henrik Koch,Tor S Haugland

doi:10.1021/acs.nanolett.1c02162

Abstract

Plasmonic nanocavities enable the confinement of molecules and electromagnetic fields within nanometric volumes. As a consequence, the molecules experience a remarkably strong interaction with the electromagnetic field to such an extent that the quantum states of the system become hybrids between light and matter: polaritons. Here, we present a nonperturbative method to simulate the emerging properties of such polaritons: it combines a high-level quantum chemical description of the molecule with a quantized description of the localized surface plasmons in the nanocavity. We apply the method to molecules of realistic complexity in a typical plasmonic nanocavity, featuring also a subnanometric asperity (picocavity). Our results disclose the effects of the mutual polarization and correlation of plasmons and molecular excitations, disregarded so far. They also quantify to what extent the molecular charge density can be manipulated by nanocavities and stand as benchmarks to guide the development of methods for molecular polaritonics.

Highlights

Plasmonic nanocavities enable the confinement of molecules and electromagnetic fields within nanometric volumes
In this work we extend the QED Coupled Cluster (QED-CC) method,[22,23] already applied to resonant optical cavities, to realistic nanoplasmonic cavities
Our goal is to describe the nanostructure at a quantum level as a material system, which differs from other approaches that quantize the electromagnetic field in the presence of dielectric media.[24,31] ε(ω)

Summary

Introduction

Plasmonic nanocavities enable the confinement of molecules and electromagnetic fields within nanometric volumes. Coupled cluster (singles and doubles excitations) is recognized as a highly accurate method in quantum chemistry:[26] we extend it to include self-consistent and correlated molecule−plasmon hybridization. With this method, we compute the interaction between a nanocavity realized after ref 18 and two realistic molecules: porphyrin and para-nitroaniline (PNA). We highlight the role of the geometrical features of the system and the role of electron−plasmon self-consistency and correlation in polaritons, beyond the standard Jaynes-Cumming picture.[27] We use PNA to quantify the same effects, already predicted on the ground and excited states electron densities[22] for a resonant cavity, in the case of a nanocavity. The dimensions of the system are about 10 × 10 nm (see Figure S1b)

Objectives

Results

Conclusion