LAUSR

Abstract We calculated the molecular orbital (MO) energies of α-Al2O3: Cr3+ (ruby) under pressure non-empirically based on one-electron calculations. The pressure was applied to the samples from ca. 0–110 GPa. Two different approaches to estimate the effect of lattice relaxation are Shannon's crystal radii method and the geometry optimization using CASTEP software. The one-electron calculations were used to estimate the MO energies, which were performed using the Discrete Variational Xα (DV-Xα) software. We found that the splitting of the crystal field (10Dq) increased as the applied pressure grew. We pointed out that collectively considering the effect of lattice relaxation and using the more substantial cluster size has a significant effect on the value of 10Dq.