Structural properties and 4f → 5d absorptions in Ce-doped LuAlO3: a first-principles study

The structural properties and the 4f -> 5d absorptions of Ce-doped LuAlO3 have been studied using the density functional theory-based generalized gradient approximation PBE + U (PBE: Perdew, Burke and Ernzerhof) and wavefunction-based embedded cluster calculations, respectively. The PBE or PBE + U calculations reveal that the substitution of Ce for Lu induces a strongly anisotropic distortion of the local atomic structure around the dopant site, which is largely insensitive to the value of U for the Ce 4f states. The calculated electronic structures depend explicitly on the value of U, and a value of U approximate to 6 eV is determined by comparison with experimental x-ray photoelectron data for CeAlO3. On the basis of the PBE-optimized structure, CASSCF/CASPT(2) (complete-active-space self-consistent-field/second-order perturbation theory) embedded cluster calculations for the Ce3+ C 4f -> 5d transitions yield energy and intensity patterns in fairly good agreement with those estimated from the experimental absorption spectrum. A Mulliken spin population analysis for the 5d(1) states shows that the origins of the states are significantly different from being caused by the cubic crystal field, confirming an earlier conclusion as regards the origin of the 5d(1) states based on semiempirical molecular orbital calculations. The importance of spin-orbit effects on the energies and wavefunctions of the Ce 5d(1) states is highlighted.