Calculation of multiplet structures of Cr3+ and V3+ in α-Al2O3 based on a hybrid method of density-functional theory and the configuration interaction

The multiplet structures of Cr3+ and V3+ in alpha-Al2O3 (alpha-Al2O3:Cr3+ and alpha-Al2O3 :V3+) have been calculated based on a hybrid method of the density-functional theory (DFT) and the configuration interaction (CI) calculation (DFT-CI approach). The correction to the electron correlation effects was estimated from the consistency between the single-electron DFT calculation and the many-electron DFT-CI calculation. The observed multiplet structures were predicted satisfactorily without referring to any experimental data. Using the explicitly obtained many-electron wave functions, the intensities of the electric-dipole transition were also calculated numerically and the polarization of the absorption spectra of alpha-Al2O3:Cr3+ (ruby) was qualitatively reproduced.