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Abstract: We analyze the basic structural units of simple reconstructions of the 111surface of SrTiO3 using density functional calculations. The prime focus is toanswer three questions: what is the most appropriate functional to use; howaccurate are the energies; what are the dominant low-energy structures andwhere do they lie on the surface phase diagram. Using test calculations ofrepresentative small molecules we compare conventional GGA with higher-ordermethods such as the TPSS meta-GGA and on-site hybrid methods PBE0 and TPSSh,the later being the most accurate. There are large effects due to reduction ofthe metal d oxygen sp hybridization when using the hybrid methods which areequivalent to a dynamical GGA+U, which leads to rather substantial improvementsin the atomization energies of simple calibration molecules, even though thed-electron density for titanium compounds is rather small. By comparing theerrors of the different methods we are able to generate an estimate of thetheoretical error, which is about 0.25eV per 1x1 unit cell, with changes of0.5-1.0 eV per 1x1 cell with the more accurate method relative to conventionalGGA. An analysis of the plausible structures reveals an unusual low-energyTiO2-rich configuration with an unexpected distorted trigonal biprismaticstructure. This structure can act as a template for layers of either TiO orTi2O3, consistent with experimental results as well as, in principle, Magnelliphases. The results also suggest that both the fracture surface and thestoichiometric SrTiO3 111 surface should spontaneously disproportionate intoSrO and TiO2 rich domains, and show that there are still surprises to be foundfor polar oxide surfaces.



Autor: Laurence D. Marks, Ann N. Chiaramonti, Fabien Tran, Peter Blaha

Fuente: https://arxiv.org/







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