Accuracy trade-off between one-electron and excitonic spectra of cuprous halides in first-principles calculations

Because of the sophisticated error cancellation in the density functional theory (DFT)-based calculations, a theoretically more accurate input would not guarantee a better output. In this work, our first-principles GW plus Bethe-Salpeter equation calculations using pseudopotentials show that cuprous halides (CuCl and CuBr) are such extreme cases for which a better one-electron band is not accompanied with a better exciton binding energy. Moreover, we find that the exchange interaction of Cu core electrons plays a crucial role in their ground-state electronic properties, especially in the energy gap and macroscopic dielectric constant. Our work provides new insights into the understanding of the electronic structure of cuprous halides from the DFT perspective.

Automated summary

This study demonstrates that despite the sophisticated error cancellation mechanism in density functional theory calculations, a more accurate input does not necessarily lead to a better output. Cuprous halides are extreme cases where an optimization of the one-electron band does not result in a better exciton binding energy. Furthermore, the exchange interaction of Cu core electrons plays a crucial role in the ground-state electronic properties of cuprous halides, particularly in the energy gap and macroscopic dielectric constant.