Optical properties of CsCu$_2$X$_3$ (X=Cl, Br and I): A comparative study between hybrid time-dependent density-functional theory and the Bethe-Salpeter equation

TL;DR

This study compares hybrid time-dependent density-functional theory and the Bethe-Salpeter equation to analyze the optical properties of cesium copper halides, highlighting hybrid TDDFT's effectiveness in capturing excitonic effects.

Contribution

It demonstrates that hybrid TDDFT with nonlocal exchange can accurately reproduce excitonic optical spectra compared to BSE, offering a promising computational approach.

Findings

Hybrid TDDFT spectra agree well with BSE results.

Nonlocal exchange influenced by dielectric constant improves accuracy.

Hybrid TDDFT is effective for excitonic effects in solids.

Abstract

The cesium copper halides CsCu$_2$X$_3$ (X=Cl, Br and I) are a class of all-inorganic perovskites with interesting and potentially useful optical properties, characterized by distinct excitonic features. We present a computational study of the optical absorption spectra of CsCu$_2$X$_3$, comparing time-dependent density-functional theory (TDDFT) and the Bethe-Salpeter equation (BSE), using $GW$ quasiparticle band structures as input. The TDDFT calculations are carried out using several types of global hybrid exchange-correlation functionals. It is found that an admixture of nonlocal exchange determined by the dielectric constant produces optical spectra in excellent agreement with the BSE. Thus, hybrid TDDFT emerges as a promising first-principles approach for excitonic effects in solids.