Systematic First-Principles Calculations of Charge Transfer Transitions of Transition Metal Ions (Sc3+, Ti3+, V3+, Cr3+, Mn3+, Fe3+) in α-Al2O3 with Structural Optimization
Shota Takemura1, Mega Novita2, Kazuyoshi Ogasawara1
1- Department of Chemistry, Kwansei Gakuin University
2- Faculty of Engineering and Informatics, Universitas PGRI Semarang
Abstract
The position of the impurity level within the band gap is very important in optical materials. It can be estimated by calculating the charge transfer transition energy from the valence band to the impurity levels (Ligand to Metal Charge Transfer: LMCT). Recently, we successfully reproduced the LMCT energies and their experimental trend of transition metal (TM) ions in α-Al2O3 using the DVME method considering the configuration-dependent correction and the lattice relaxation based on the Shannons crystal radii. We also clarified that the LMCT energy is very sensitive to the bond length. In this work, in order to calculate the LMCT energies for various trivalent TM ions in α-Al2O3 using more accurate model clusters, we performed structural optimization using the CASTEP code and constructed the optimized TMO69- and TMAl13O630+ clusters (TM = Sc3+, Ti3+, V3+, Cr3+, Mn3+, Fe3+). As a result, the trend from Sc to V was reproduced better by calculations using the optimized clusters. The differences between the LMCT energies of the optimized clusters and those of the relaxed clusters based on the crystal radii originate from the multiplet splitting of the LMCT states.
Keywords: Charge transfer transition, Multiplet, Structural optimization
Topic: DV-Xa Method