First principles calculations of SrZrO₃ bulk and ZrO₂-terminated (001) surface F centers

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• 作者：R.I. Eglitis ; ^{rieglitis@gmail.com" class="auth_mail" title="E-mail the corresponding author} ; S. Piskunov
• 关键词：Ab initio calculations ; SrZrO3 ; Bulk F center ; (001) surface F-Center
• 刊名：Computational Condensed Matter
• 出版年：2016
• 出版时间：June 2016
• 年：2016
• 卷：7
• 期：Complete
• 页码：1-6
• 全文大小：1778 K

文摘

Using a supercell model and B3PW hybrid exchange-correlation functional in the framework of the density functional theory (DFT), as it is implemented in the CRYSTAL computer code, we performed ab initio calculations for the F-center located in the SrZrO₃ bulk and on the ZrO₂-terminated (001) surface. According to the results of performed relaxation of atoms around the defect, two nearest Zr and four Sr atoms are repulsed, but all oxygen atoms are attracted towards both, the bulk and (001) surface F-center. The displacement magnitudes of atoms surrounding the bulk F-center are smaller than around the (001) surface F-center. The B3PW calculated SrZrO₃ bulk optical band gap (5.00 eV) is in a fair agreement with the experimental value of 5.6 eV. The ZrO₂-terminated (001) surface optical band gap (4.63 eV) is smaller in regard to the bulk value. The bulk and (001) surface F-center bands in SrZrO₃, calculated using 3 × 3 × 3 and 3 × 3 × 1 times expanded supercells, are located 1.12 and 0.93 eV under the conduction band bottom. The O vacancy in the SrZrO₃ bulk attracts 1.25e, and even less, only 1.10e on the ZrO₂-terminated (001) surface. Performed calculations reveal significant enhancement of the chemical bond covalency among the SrZrO₃ bulk F-center and its nearest Zr atoms of 0.244e in comparison with the ideal SrZrO₃ perovskite Zralt="single bond" data-inlimg="/entities/sbnd" src="/sd/grey_pxl.gif" class="glyphImg imgLazyJSB">O chemical bond covalency of 0.100e. Our detected defect formation energy for the F-center located on the ZrO₂-terminated (001) surface 7.52 eV is somewhat smaller than in the SrZrO₃ bulk 7.55 eV. Our calculated formation energy difference may trigger the segregation of the F-center from the SrZrO₃ bulk towards the ZrO₂-terminated (001) surface.