DFT+U calculation of the Cr K pre-edge structures in ZnCr2O4

Abstract

Zinc chromite ZnCr2O4 has been investigated by X-ray absorption near edge structure (XANES) spectroscopy at the Cr K-edge, with the objective of better understanding the origin of the electronic excitations giving rise to the pre-edge features. In particular, the origin of a third feature visible only in Cr-rich compounds of the ZnAl2O4-ZnCr2O4 solid solution is studied. Standard density functional theory (DFT) XANES calculations were first performed, then a Hubbard U parameter was included in an attempt to improve the relative peak positions by increasing the localization of the Cr 3d states. The origin of the pre-edge features in ZnCr2O4 has been analyzed using DFT+U calculations, local projected densities of states and the assignment of the spectral features for the dilute ZnAl2O4:Cr3+ compound. We show that DFT+U does not overcome the limitations of standard DFT in modeling the relative peak positions, and that approaches including advanced description of the electron-hole interaction are needed.