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Tuning LDA+U for electron localization and structure at oxygen vacancies in ceria
Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
Department of Materials Chemistry, Uppsala University, Box 538, SE-75121, Sweden.
Department of Materials Chemistry, Uppsala University, Box 538, SE-75121, Sweden.
2007 (English)In: Journal of Chemical Physics, ISSN 0021-9606, Vol. 127, no 24Article in journal (Refereed) Published
Abstract [en]

We examine the real space structure and the electronic structure (particularly Ce4f electron localization) of oxygen vacancies in Ce O2 (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 Ce O2 and Ce2 O3, with and without vacancies, is hard to find. © 2007 American Institute of Physics.

Place, publisher, year, edition, pages
2007. Vol. 127, no 24
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-47643DOI: 10.1063/1.2800015OAI: diva2:268539
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2011-01-11

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Castleton, Christopher
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