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J. Atanelov, C. Gruber, P. Mohn:
"The electronic and magnetic structure of p-element (C,N) doped rutile-TiO₂; a hybrid DFT study";
Computational Materials Science, 98 (2015), 15 - 21.

We study the electronic and magnetic structure of carbon and nitrogen impurities and interstitials in
rutile TiO2. To this end we perform ab initio calculations of a 48-atom supercell employing the VASP code.
In order to obtain a realistic description of the electronic and magnetic structure, exchange and correlation
are treated with the HSE06 hybrid functional. Both, atomic positions and cell dimensions are fully
relaxed. Substitutional carbon and nitrogen are found to have a magnetic moment of 2 and 1lB, respectively,
with a tendency for anti-ferromagnetic long range order. For C/N on interstitial sites we find that
carbon is non-magnetic while nitrogen always possesses a magnetic moment of 1lB. We find that these
interstitial positions are on a saddle point of the total energy. The stable configuration is reached when
both carbon and nitrogen form a C-O and N-O dimer with a bond length close to the double bond for CO
and NO. This result is in agreement with earlier experimental investigations detecting such N-O entities
from XPS measurements. The frequencies of the symmetric stretching mode are calculated for these
dimers, which could provide a means for experimental verification. For all configurations investigated
both C and N states are found inside the TiO2 gap. These new electronic states are discussed with respect
to tuning doped TiO2 for the application in photocatalysis.