Electronic and optical properties of rare earth trifluorides RF3 (R = La, Ce, Pr, Nd, Gd and Dy)

This work presents the electronic structure and optical properties of some rare earth trifluorides (RF3) coarsely covering a large range of rare-earths with R = La, Ce, Pr, Nd, Gd and Dy. Our theoretical investigations are based on the first principles, using the full potential linearized augmented plane wave method with the inclusion of spin orbit coupling. The local spin density approximation (LSDA) and the Coulomb-corrected LSDA + U method have been employed. We find that the standard LSDA approach is incapable of correctly describing the electronic properties of such materials since it positions the f-bands incorrectly resulting in an incorrect metallic ground state. On the other hand, LSDA + U approximation, known for treating the highly correlated 4f electrons properly, is able to reproduce the correct insulating ground state. Interestingly, however, we do not find any significant differences in the optical properties calculated using LSDA and LSDA + U suggesting that the 4f electrons do not play a decisive role in the optical properties of these compounds. The reflectivity for all the compounds stays low till ∼7 eV which is consistent with their large energy gaps. The calculated energy gaps are in good agreement with experiments. Our calculated reflectivity compares well with the experimental data and the results are analyzed in the light of band to band transitions.