Abstract
There are many examples of defects in strongly-correlated metal oxides for which density functional theory predicts electronic structures that qualitatively disagree with experimental data. This behaviour arises from the self-interaction error inherent to standard density functionals, and is demonstrated by both p- and n-type systems where the defect state is a small polaron associated with host lattice atoms. An approximate correction is to describe the electron—electron interactions in the orbitals of interest within the DFT+U formalism. This gives improved descriptions for systems where the states of interest are well represented by atomic-like orbitals. The qualitative failure of standard DFT and corresponding improvement achieved with DFT+U is illustrated for cases where the defect state is primarily associated with localised cation f and d states (O vacancies in CeO2 and TiO2) and anion p states (Li-doped MgO). [DOI: 10.1380/ejssnt.2009.389]
Highlights
Numerous metal oxide surfaces are technologically useful as heterogeneous catalysts
In this paper we describe three defective metal oxide systems that are widely used in catalytic technologies, and which illustrate the applicability of the DFT+U methodology to obtaining descriptions that are in qualitative agreement with experimental data [16]
There are numerous technologically useful surface systems where chemically active defects are characterised by small polaronic states
Summary
The Use of the “+U ” Correction in Describing Defect States at Metal Oxide Surfaces: Oxygen Vacancies on CeO2 and TiO2, and Li-doping of MgO∗. There are many examples of defects in strongly-correlated metal oxides for which density functional theory predicts electronic structures that qualitatively disagree with experimental data. This behaviour arises from the self-interaction error inherent to standard density functionals, and is demonstrated by both p- and n-type systems where the defect state is a small polaron associated with host lattice atoms. An approximate correction is to describe the electron–electron interactions in the orbitals of interest within the DFT+U formalism This gives improved descriptions for systems where the states of interest are well represented by atomic-like orbitals.
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