Multi-gap absorption in CaCu$_{3}$Ti$_{4}$O$_{12}$ and the predictivity of ab initio methods

TL;DR

This study investigates the electronic structure of CaCu$_{3}$Ti$_{4}$O$_{12}$ using various ab initio methods, providing new insights into its optical transitions and evaluating the accuracy of computational approaches.

Contribution

It offers a new interpretation of optical spectra and assesses the predictivity of different density-functional methods for this complex material.

Findings

Four distinct optical transitions identified around 0.7, 1.5, 2.5, and 3.5 eV.

Spin disorder affects transition intensities without closing the fundamental gap.

Some computational methods tend to overestimate electronic band gaps.

Abstract

We report the electronic properties of the quadruple perovskite CaCu$_{3}$Ti$_{4}$O$_{12}$ as obtained via several density-functional based methods, and propose a new interpretation of optical experiments to the effect that four distinct transitions (centered around 0.7, 1.5, 2.5, and 3.5 eV) contribute to the spectrum. The comparison with experiment is satisfactory, especially after we account for the effects of spin disorder, which does not close the fundamental gap but suppresses the transition intensity. We find that some of the methods we employ tend to overestimate considerably the gaps for standard values of the respective adjustable parameters.