Excitonic effects on infrared vibrational and Raman spectroscopy from first principles

TL;DR

This paper introduces a first-principles method to include excitonic effects in IR and Raman spectra calculations, enabling accurate analysis of vibrational properties in 2D materials.

Contribution

It develops a perturbative approach within TD-aGW theory to incorporate excitonic effects into IR and Raman spectra from first principles.

Findings

Significant excitonic enhancement observed in IR and Raman spectra of monolayer TMDs.

Method allows access to exciton-phonon coupling strength and exciton energy landscape.

Approach agrees with diagrammatic methods for Raman spectrum.

Abstract

We develop a first-principles approach to compute infrared (IR) vibrational absorption and Raman scattering spectra with excitonic effects included. Our method is based on a perturbative expansion of electron-phonon and electron-light couplings in the time-dependent adiabatic GW (TD-aGW) theory. We show that excitonic effects in the IR absorption spectrum can be included by replacing the free electron-hole propagators in the perturbative expression for independent particles with their interacting counterparts, which are readily available from standard GW-Bethe-Salpeter equation calculations. For Raman spectrum, our derived expression agrees with the single and double resonance terms from a diagrammatic approach. We show significant excitonic enhancement in both the IR and resonance Raman scattering intensity for monolayer MoS2, WS2, and WSe2. Moreover, the exciton-phonon coupling strength and exciton energy landscape can be accessed by analyzing resonance Raman spectrum of these materials.