Tuning LDA+U for electron localization and structure at oxygen vacancies in ceria
2007 (English)In: Journal of Chemical Physics, ISSN 0021-9606, Vol. 127, no 24, 244704-244704-11 p.Article in journal (Refereed) Published
We examine the real space structure and the electronic structure (particularly Ce4f electron localization) of oxygen vacancies in CeO2 (ceria) as a function of U in density functional theory studies with the rotationally invariant forms of the LDA+U and GGA+U functionals. The four nearest neighbor Ce ions always relax outwards, with those not carrying localized Ce4f charge moving furthest. Several quantification schemes show that the charge starts to become localized at U~3 eV and that the degree of localization reaches a maximum at ~6 eV for LDA+U or at ~5.5 eV for GGA+U. For higher U it decreases rapidly as charge is transferred onto second neighbor O ions and beyond. The localization is never into atomic corelike states; at maximum localization about 80-90% of the Ce4f charge is located on the two nearest neighboring Ce ions. However, if we look at the total atomic charge we find that the two ions only make a net gain of (0.2-0.4)e each, so localization is actually very incomplete, with localization of Ce4f electrons coming at the expense of moving other electrons off the Ce ions. We have also revisited some properties of defect-free ceria and find that with LDA+U the crystal structure is actually best described with U=3-4 eV, while the experimental band structure is obtained with U=7-8 eV. (For GGA+U the lattice parameters worsen for U>0 eV, but the band structure is similar to LDA+U.) The best overall choice is U~6 eV with LDA+U and ~5.5 eV for GGA+U, since the localization is most important, but a consistent choice for both CeO2 and Ce2O3, with and without vacancies, is hard to find.
Place, publisher, year, edition, pages
2007. Vol. 127, no 24, 244704-244704-11 p.
Other nonmetals, Point defects and defect clusters, Density functional theory, local density approximation, gradient and other corrections
IdentifiersURN: urn:nbn:se:uu:diva-12806DOI: 10.1063/1.2800015ISI: 000251987800030OAI: oai:DiVA.org:uu-12806DiVA: diva2:40575