Investigation of the multiplet structures and crystal field effects of a TiO₆ 3d¹ cluster based on configuration interaction calculations

Configuration interaction cluster calculation can effectively reproduce the experimentally measured Ti L₂₃-edge absorption spectrum for the TiO₆ cluster LaTiO₃. A further investigation of the hybridization strength and charge-transfer energy effects on the multiplet structures suggests that LaTiO₃ should be classified as an intermediate state between the charge-transfer and Mott–Hubbard regimes. Detailed temperature-dependent simulations of absorption spectra support the lifting of Ti t_2g orbital degeneracy and crystal field splitting. The spin–orbit coupling scenario is ruled out, even though 3d spin–orbit coupling can reproduce the experimental spectrum without including temperature. A combined polarization- and crystal-field-splitting-dependent analysis indicates asymmetric Δ_CF–orbital interactions for the TiO₆ cluster [Ti³⁺:3d¹(t_2g¹)], different from the orbital–lattice interactions reported for the NiO₆ cluster [Ni³⁺:3d⁷(t_2g⁶e_g¹)]. The orbital polarization is defined in terms of the normalized electron occupancies in orbitals with xy and xz(yz) symmetries, and nearly complete orbital polarization (more than 75%) is observed, indicating strongly reduced orbital fluctuations due to the correlation effects. This is consistent with the density of states for titanates based on local density approximation plus dynamical mean-field theory calculations.