In ceria the formation of oxygen vacancies played a key role. Density functional theory, corrected for on-site Coulomb interactions (DFT + U) provided a reasonable description of oxygen vacancies, but had issues with the U dependence. A hybrid HSE06 study was made of oxygen vacancies in the (110) and (100) ceria surfaces. It was found that the oxygen vacancy formation energy was larger with hybrid DFT compared with DFT + U, that localised Ce3+ ions formed and that the position of the Ce3+ gap state was in good agreement with experiment. The results provided important information for assessing the reliability of the DFT + U approach.

Hybrid Density Functional Theory Description of Oxygen Vacancies in the CeO2 (110) and (100) Surfaces. M.Nolan: Chemical Physics Letters, 2010, 499[1-3], 126-30