Frontier Orbitals and Quasiparticle Energy Levels in Ionic Liquids

TL;DR

This paper demonstrates that GW calculations accurately determine the quasiparticle energy levels of ionic liquids, outperforming mean-field methods and aligning well with experimental spectra, thus enhancing understanding of their electronic properties.

Contribution

The study applies first-principles GW calculations to ionic liquids, showing their superiority over mean-field approaches in predicting electronic energy levels.

Findings

GW results agree with experimental photoelectron spectra

Mean-field methods show qualitative and quantitative discrepancies

GW provides a reliable tool for ionic liquid electronic structure analysis

Abstract

Room temperature ionic liquids play an important role in many technological applications and a detailed understanding of their frontier molecular orbitals is required to optimize interfacial barriers, reactivity and stability with respect to electron injection and removal. In this work, we calculate quasiparticle energy levels of ionic liquids using first-principles many-body perturbation theory within the GW approximation and compare our results to various mean-field approaches, including semilocal and hybrid density-functional theory and Hartree-Fock. We find that the mean-field results depend qualitatively and quantitatively on the treatment of exchange-correlation effects, while GW calculations produce results that are in excellent agreement with experimental photoelectron spectra of gas phase ion pairs and ionic liquids. These results establish the GW approach as a valuable tool for understanding the electronic structures of ionic liquids.