A DFT + U description of oxygen vacancies at the TiO2 rutile (1 1 0) surface |
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Authors: | Benjamin J. Morgan |
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Affiliation: | School of Chemistry, Trinity College, University of Dublin, Dublin 2, Ireland |
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Abstract: | Experimental observations indicate that removing bridging oxygen atoms from the TiO2 rutile (1 1 0) surface produces a localised state approximately 0.7 eV below the conduction band. The corresponding excess electron density is thought to localise on the pair of Ti atoms neighbouring the vacancy; formally giving two Ti3+ sites. We consider the electronic structure and geometry of the oxygen deficient TiO2 rutile (1 1 0) surface using both gradient-corrected density functional theory (GGA DFT) and DFT corrected for on-site Coulomb interactions (GGA + U) to allow a direct comparison of the two methods. We show that GGA fails to predict the experimentally observed electronic structure, in agreement with previous uncorrected DFT calculations on this system. Introducing the +U term encourages localisation of the excess electronic charge, with the qualitative distribution depending on the value of U. For low values of U (?4.0 eV) the charge localises in the sub-surface layers occupied in the GGA solution at arbitrary Ti sites, whereas higher values of U (?4.2 eV) predict strong localisation with the excess electronic charge mainly on the two Ti atoms neighbouring the vacancy. The precise charge distribution for these larger U values is found to differ from that predicted by previous hybrid-DFT calculations. |
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Keywords: | Ab initio quantum chemical methods and calculations Density functional calculations Titanium oxide Surface defects Self-interaction correction, Surface electronic phenomena |
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