The cesium copper halides ${\mathrm{CsCu}}_2{X}_3$ $(X=\mathrm{Cl}, \mathrm{Br}, \mathrm{and} \mathrm{I})$ 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 ${\mathrm{CsCu}}_2{X}_3$, 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.

• Received 24 July 2020
• Accepted 2 September 2020

DOI:https://doi.org/10.1103/PhysRevMaterials.4.095402