Suchergebnisse

We greatly acknowledge the financial support via the ERAF Project No. 1.1.1.1/18/A/073. Calculations were performed using Latvian Super Cluster (LASC), located in the Center of Excellence at Institute of Solid State Physics, the University of Latvia, which is supported by European Union Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-Teaming Phase 2 under Grant Agreement No. 739508, project CAMART. ; We performed, to the best of our knowledge, the world's first first-principles calculations for the WO2-terminated cubic WO3 (001) surface and analyzed the systematic trends in the WO3, SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (001) surface ab initio calculations. According to our first principles calculations, all WO2 or TiO2-terminated WO3, SrTiO3, BaTiO3, PbTiO3 and CaZrO3 (001) surface upper-layer atoms relax inwards towards the crystal bulk, while all second-layer atoms relax upwards. The only two exceptions are outward relaxations of first layer WO2 and TiO2-terminated WO3 and PbTiO3 (001) surface O atoms. The WO2 or TiO2-terminated WO3, SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (001) surface-band gaps at the Γ–Γ point are smaller than their respective bulk-band gaps. The Ti–O chemical bond populations in the SrTiO3, BaTiO3, PbTiO3 and CaTiO3 bulk are smaller than those near the TiO2-terminated (001) surfaces. Conversely, the W–O chemical bond population in the WO3 bulk is larger than near the WO2-terminated WO3 (001) surface.---//---This work is licensed under a CC BY 4.0 license. ; ERAF Project No. 1.1.1.1/18/A/073; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART².

Valuable discussions with E. A. Kotomin are gratefully acknowledged. Research contribution of R. E. and A. I. P. has been performed within the framework of the EUROfusion Enabling Research project: ENR-MFE19.ISSP-UL-02 "Advanced experimental and theoretical analysis of defect evolution and structural disordering in optical and dielectric materials for fusion applications." The views and opinions expressed herein do not necessarily reflect those of the European Commission. ; We report the results of ab initio calculations and analysis of systematic trends for the F centers in the bulk and on the (001) surface in oxide perovskites, such as BaTiO3, SrTiO3, SrZrO3, and PbZrO3, with a corresponding comparison of the F centers in perovskites with those in alkaline earth metal fluorides (CaF2, BaF2, and SrF2). It was found that in perovskites in both bulk F centers and those on their (001) surfaces, two nearest to the vacancy Ti or Zr atoms repel each other, while the next nearest O atoms relax towards the oxygen vacancy. It was also found that the obtained relaxations of atoms in the nearest neighborhood around the F center in ABO3 perovskites are generally larger than in alkaline earth metal fluorides. The bulk and (001)-terminated surface F center ground states in BaTiO3, SrTiO3, and SrZrO3 perovskites are located 0.23, 0.69, 1.12 eV, and 0.07, 0.25, 0.93 eV, respectively, below the conduction band bottom, indicating that the F center is a shallow donor. The vacancies in BaTiO3, SrZrO3, and PbZrO3 are occupied with 1.103e, 1.25e, and 0.68e, respectively, whereas slightly smaller charges, only 1.052e, 1.10e, and 0.3e are localized inside the F center on the perovskite (001) surface. In contrast to the partly covalent ABO3 perovskites, charge is well localized (around 80%) inside the ionic CaF2, BaF2, and SrF2 fluorine vacancy. --- / / / --- This is the preprint version of the following article: R. Eglitis, A. I. Popov, J. Purans and Ran Jia,First principles hybrid Hartree-Fock-DFT calculations of bulk and (001) surface F centers in oxide perovskites and alkaline-earth fluorides, Low Temperature Physics,46, 1206 (2020), DOI ttps://doi.org/10.1063/10.0002475, which has been published in final form at https://aip.scitation.org/doi/10.1063/10.0002475. This article may be used for non-commercial purposes in accordance with American Institute of Physics terms and conditions for sharing and self-archiving. ; EUROfusion Enabling Research project: ENR-MFE19.ISSP-UL-02; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART².

We greatly acknowledge the financial support via Latvian-Ukrainian Joint Research Project No. LV-UA/2018/2, Latvian Council of Science Grant No. 2018/2-0083 "Theoretical prediction of hybrid nanostructured photocatalytic materials for efficient water splitting", Latvian Council of Science Grant No. 2018/1-0214 as well as ERAF Project No. 1.1.1.1/18/A/073. ; The paper presents and discusses the results of performed calculations for YAlO3 (111) surfaces using a hybrid B3LYP description of exchange and correlation. Calculation results for SrTiO3, BaTiO3 and BaZrO3 (111) as well as YAlO3, SrTiO3, BaTiO3 and BaZrO3 (001) surfaces are listed for comparison purposes in order to point out systematic trends common for these four ABO3 perovskite (001) and (111) surfaces. According to performed ab initio calculations, the displacement of (001) and (111) surface metal atoms of YAlO3, SrTiO3, BaTiO3 and BaZrO3 perovskite, upper three surface layers for both AO and BO2 (001) as well as AO3 and B (111) surface terminations, in most cases, are considerably larger than that of oxygen atoms. The YAlO3, SrTiO3, BaTiO3 and BaZrO3 (001) surface energies for both calculated terminations, in most cases, are almost equal. In contrast, the (111) surface energies for both AO3 and B-terminations are quite different. Calculated (111) surface energies always are much larger than the (001) surface energies. As follows from performed ab initio calculations for YAlO3, SrTiO3, BaTiO3 and BaZrO3 perovskites, the AO- and BO2-terminated (001) as well as AO3- and B-terminated (111) surface bandgaps are almost always reduced with respect to their bulk bandgap values. --- / / / --- This is the preprint version of the following article: Roberts Eglitis, J. Purans, A. I. Popov and Ran Jia,Systematic trends in YAlO3, SrTiO3, BaTiO3, BaZrO3 (001) and (111) surface ab initio calculations, JInternational Journal of Modern Physics B, Vol. 33, No. 32 (2019) 1950390, DOI https://doi.org/10.1142/S0217979219503909, which has been published in final form at https://www.worldscientific.com/doi/abs/10.1142/S0217979219503909. This article may be used for non-commercial purposes in accordance with World Scientific Publishing Terms and Conditions for Sharing and Self-Archiving. The copyright of this work belongs to the publisher. ; Latvian-Ukrainian Joint Research Project No. LV-UA/2018/2; Latvian Council of Science Grant No. 2018/2-0083; Latvian Council of Science Grant No. 2018/1-0214; ERAF Project No. 1.1.1.1/18/A/073; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART².

Financial support via Latvian-Ukrainian Joint Research Project No. LV-UA/2018/2 for A. I. Popov, Latvian Council of Science Project No. 2018/2-0083 "Theoretical prediction of hybrid nanostructured photocatalytic materials for efficient water splitting" for R. I. Eglitis and J. Kleperis as well as ERAF project No. 1.1.1.1/18/A/073 for R. I. Eglitis and J. Purans is greatly acknowledged. ; By means of the CRYSTAL computer program package, first-principles calculations of polar ZrO-, Ca- and O-terminated CaZrO3 (011) surfaces were performed. Our calculation results for polar CaZrO3 (011) surfaces are compared with the previous ab initio calculation results for ABO3 perovskite (011) and (001) surfaces. From the results of our hybrid B3LYP calculations, all upper-layer atoms on the ZrO-, Ca- and O-terminated CaZrO3 (011) surfaces relax inwards. The only exception from this systematic trend is outward relaxation of the oxygen atom on the ZrO-terminated CaZrO3 (011) surface. Different ZrO, Ca and O terminations of the CaZrO3 (011) surface lead to a quite different surface energies of 3.46, 1.49, and 2.08 eV. Our calculations predict a considerable increase in the Zr–O chemical bond covalency near the CaZrO3 (011) surface, both in the directions perpendicular to the surface (0.240e) as well as in the plane (0.138e), as compared to the CaZrO3 (001) surface (0.102e) and to the bulk (0.086e). Such increase in the B–O chemical bond population from the bulk towards the (001) and especially (011) surfaces is a systematic trend in all our eight calculated ABO3 perovskites. This work is licensed under a CC BY license. ; Latvian-Ukrainian Joint Research Project No. LV-UA/2018/2; Latvian Council of Science Project No. 2018/2-0083; ERAF project No. 1.1.1.1/18/A/073; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART².

We greatly acknowledge the financial support via the ERAF Project No. 1.1.1.1/18/A/073. ; We performed, for first time, ab initio calculations for the ReO2-terminated ReO3 (001) surface and analyzed systematic trends in the ReO3, SrZrO3, BaZrO3, PbZrO3 and CaZrO3 (001) surfaces using first-principles calculations. According to the ab initio calculation results, all ReO3, SrZrO3, BaZrO3, PbZrO3 and CaZrO3 (001) surface upper-layer atoms relax inwards towards the crystal bulk, all second-layer atoms relax upwards and all third-layer atoms, again, relax inwards. The ReO2-terminated ReO3 and ZrO2-terminated SrZrO3, BaZrO3, PbZrO3 and CaZrO3 (001) surface band gaps at the Γ–Γ point are always reduced in comparison to their bulk band gap values. The Zr–O chemical bond populations in the SrZrO3, BaZrO3, PbZrO3 and CaZrO3 perovskite bulk are always smaller than those near the ZrO2-terminated (001) surfaces. In contrast, the Re–O chemical bond population in the ReO3 bulk (0.212e) is larger than that near the ReO2-terminated ReO3 (001) surface (0.170e). Nevertheless, the Re–O chemical bond population between the Re atom located on the ReO2-terminated ReO3 (001) surface upper layer and the O atom located on the ReO2-terminated ReO3 (001) surface second layer (0.262e) is the largest. ; Latvian Government ERAF Grant number 1.1.1.1/18/A/073; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

Previously, Ren et al. [Chem. Phys. 518, 69–73, 2019] reported the failure of Boron-Nitrogen (B-N) co-doping as inter B-N bond in T-carbon. In present work, a B-N atom pair is introduced in T-carbon as p-n co-dopant to substitute two carbon atoms in the same carbon tetrahedron and form an intra B-N bond. The stability of this doping system is verified from energy, lattice dynamic, and thermodynamic aspects. According to our B3PW calculations, B-N impurities in this situation can reduce the band gap of T-carbon from 2.95 eV to 2.55 eV, making this material to be a promising photocatalyst. Through the study of its transport properties, we can also conclude that B-N co-doping cannot improve the thermoelectric performance of T-carbon. ; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

This work is supported by National Natural Science Foundation of China (Grant No. 21173096). ; The singly B and N doped graphene systems are carefully studied. The highly concentrated dopants cause a spin polarization effect in the systems. The spin polarization limits are affirmed in the singly B and N doped graphene systems through periodic hybrid density functional theory studies. The spin polarization effects must be considered indeed in the B and N doped graphene systems if the dopant concentration is above 3.1% and 1.4%, respectively. The system symmetry cooperating with the presence of the spin polarization brings half-metallic properties into the doping systems. The semiconducting channels in the half-metallic systems are in two different spin directions due to the different electron configurations of the B and N dopants in graphene. ; National Natural Science Foundation of China 21173096; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²