Nature of the electronic band gap in lanthanide oxides

Accurate electronic structures of the technologically important lanthanide/rare-earth sesquioxides (Ln sub(2)O sub(3), with Ln = La, ... ,Lu) and CeO sub(2) have been calculated using hybrid density functionals HSE03, HSE06, and screened exchange (sX-LDA). We find that these density functional methods describe the strongly correlated Ln [functionof] electrons as well as the recent G sub(0)W sub(0)LDA+U results, generally yielding the correct band gaps and trends across the Ln period. For HSE, the band gap between O 2p states and lanthanide 5d states is nearly independent of the lanthanide, while the minimum gap varies as filled or empty Ln 4[functionof] states come into this gap. sX-LDA predicts the unoccupied 4[functionof] levels at higher energies, which leads to a better agreement with experiments for Sm sub(2) O sub(3), Eu sub(2)O sub(3), and Yb sub(2)O sub(3).