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Comparative ab initio calculations of SrTiO 3 and CaTiO 3 polar (111) surfaces
Author(s) -
Eglitis R. I.
Publication year - 2015
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201248072
Subject(s) - materials science , ab initio , ab initio quantum chemistry methods , band gap , atom (system on chip) , strontium titanate , relaxation (psychology) , polar , condensed matter physics , thin film , chemistry , nanotechnology , molecule , physics , optoelectronics , organic chemistry , computer science , embedded system , psychology , social psychology , astronomy
We present the results of calculations of SrTiO 3 and CaTiO 3 polar (111) surface relaxations, rumplings, energetics, optical band gaps, and charge distributions using the ab initio code CRYSTAL and a hybrid description of exchange and correlation. We have calculated the surface relaxation of the two possible terminations (Ti and SrO 3 or CaO 3 ) of the SrTiO 3 and CaTiO 3 (111) surfaces. According to our calculations, atoms of the first surface layer relax inwards for Ti‐, SrO 3 ‐, and CaO 3 ‐terminated (111) surfaces of both materials. The only exception is outward relaxation of the SrO 3 ‐terminated SrTiO 3 (111) surface upper layer Sr atom. For both Ti‐terminated SrTiO 3 and CaTiO 3 (111) surfaces our calculated second layer Sr and Ca metal atom inward relaxations are approximately four and two times larger than the upper layer Ti atom inward relaxation. Our calculated optical band gap for the SrO 3 ‐ and Ti‐terminated SrTiO 3 , as well as for CaO 3 ‐terminated CaTiO 3 (111) surfaces, becomes smaller with respect to the bulk optical band gap. Our calculated surface energies for SrO 3 ‐ and CaO 3 ‐terminated SrTiO 3 and CaTiO 3 (111) surfaces (6.30 and 5.86 eV) are considerably larger than the surface energies for Ti‐terminated SrTiO 3 and CaTiO 3 (111) surfaces (4.99 and 4.18 eV). Our B3LYP calculations indicate a considerable increase of Ti–O chemical bond covalency near the SrTiO 3 and CaTiO 3 (111) surface (+0.098 e and +0.094 e ) relative to the SrTiO 3 and CaTiO 3 bulk (+0.088 e and +0.084 e ).