0000000000161837
AUTHOR
Alexander Platonenko
Site symmetry approach applied to the supercell model of MgAl2O4 spinel with oxygen interstitials: Ab initio calculations
This study has been carried out within the framework of the EUROfusion Consortium and has been provided funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The authors are indebted to E.A. Kotomin, A.I. Popov and R. Vila for stimulating discussions. The views and opinions expressed herein do not necessarily reflect those of the European Commission. Calculations have been performed using both the Marconi supercomputer system at the Computational Simulation Centre (Italy) and the Computer Center of St. Petersburg State University.
Vacancy Defects in Ga2O3: First-Principles Calculations of Electronic Structure
This research was funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (Grant No. AP08856540) as well as by the Latvian research council via the Latvian National Research Program under the topic ?High-Energy Physics and Accelerator Technologies?, Agreement No: VPP-IZM-CERN-2020/1-0002 for A.I. Popov. In addition, J. Purans is grateful to the ERAF project 1.1.1.1/20/A/057 while A. Platonenko was supported by Latvian Research Council No. LZP-2018/1-0214. The authors thank A. Lushchik and M. Lushchik for many useful discussions. The research was (partly) performed in the Institute of Solid State Physics, University of Latvia ISSP UL. ISSP UL as…
First-principles calculations on Fe-Pt nanoclusters of various morphologies
Financial support provided by Scientific Research Project for Students and Young Researchers Nr. SJZ/2016/17 implemented at the Institute of Solid State Physics, University of Latvia, is greatly acknowledged. A.P. and R.E. express their gratitude to High-performance computer centers of ISSP (University of Latvia) and St. Petersburg University. This research was partially supported by Graphene Flagship GrapheneCore1-AMD-696656-4.
Charged oxygen interstitials in corundum: first principles simulations
Combining supercell models and hybrid B3PW exchange-correlation functionals, ab initio simulations on quasi-stable configurations of interstitial ions in α-Al2O3 (corundum) crystals and possible migration trajectories have been modelled. We have studied crystalline distortion around migrating including interatomic distances and the effective atomic charges, as well as redistributions of the electronic density. Unlike neutral interstitial atom Oi studied by us previously, migrating ion does not form dumbbells with the nearest regular oxygen ions, due to the strong Coulomb interaction with the nearest cations as well as stronger repulsion between and adjacent regular ions. We have also estima…
Interstitial defects in diamond: A quantum mechanical simulation of their EPR constants and vibrational spectra
The local geometry, electronic structure, and vibrational features of three vicinal double interstitial defects in diamond, ICIC, ICIN, and ININ, are investigated and compared with those of three "simple" ⟨100⟩ interstitial defects, ICC, ICN, and INN, previously reported by Salustro et al. [Phys. Chem. Chem. Phys. 20, 16615 (2018)], using a similar quantum mechanical approach based on the B3LYP functional constructed from Gaussian-type basis sets, within a supercell scheme, as implemented in the CRYSTAL code. For the first time, the Fermi contact term and hyperfine coupling tensor B of the four open shell structures, ICIC, ICIN, ICC, and ICN, are evaluated and compared with the available ex…
Nitrogen interstitial defects in silicon. A quantum mechanical investigation of the structural, electronic and vibrational properties
The vibrational features of eight interstitial nitrogen related defects in silicon have been investigated at the first principles quantum mechanical level by using a periodic supercell approach, a hybrid functionals, an all electron Gaussian type basis set and the Crystal code. The list includes defects that will be indicated as Ni (one N atom forming a bridge between two Si atoms), Ni-Ns (one interstitial and one substitutional N atom linked to the same Si atom), Ni-Ni (two Ni defects linked to the same couple of silicon atoms) and Ni-Sii-Ni (two Ni defects linked to the same interstitial silicon atom). Four 〈0 0 1〉 split interstitial (dumbbell) defects have also been considered, in which …
First principles simulations on migration paths of oxygen interstitials in magnesium aluminate spinel
This study has been carried out within the framework of the EURO fusion Consortium and has been provided funding from the Euratom research and training program 2014–2018 under grant agreement No. 633053. The authors are indebted to A.I. Popov, A.C. Lushchik and R. Vila for stimulating discussions. Technical assistance from O. Lisovski is appreciated too. The views and opinions expressed herein do not necessarily reflect those of the European Commission. Calculations have been performed using Marconi supercomputer system based in Italy at CINECA Supercomputing Centre.
Atomic, electronic and magnetic structure of an oxygen interstitial in neutron-irradiated Al2O3 single crystals
This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under Grant Agreement No. 633053 and 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 application”. The views and opinions expressed herein do not necessarily reflect those of the European Commission. In addition, the research leading to these results has received funding from the Estonian Research Council grant (PUT PRG619).
Ab initio simulations on Frenkel pairs of radiation defects in corundum
Large scale first principles periodic calculations based on the density functional theory within the localized atomic orbital approach (DFT-LCAO) using the hybrid exchange- correlation potential B3PW have been performed in order to study the structural and electronic properties of radiation-induced Frenkel pairs Oi+VO in corundum crystal. As an initial approach, we have used conventional 2x2x1 supercell for defective α-Al2O3 lattice containing 120 atoms. After relaxation of the ideal supercell structure, the optimized doi-vo distance has been found to be ~4.5 A while the formation energy of Frenkel pair has achieved 11.7 eV. The interstitial Oi atom, both single and a component of Oi+VO pai…
First-principles calculations of oxygen interstitials in corundum: a site symmetry approach
The authors are indebted to R. Vila, A. Popov and A. Lushchik for stimulating discussions. This work was carried out within the framework of the EUROfusion Consortium and received funding from the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. Support from Latvian National Research Program IMIS2 (2014–2017) is also appreciated. Calculations were carried out using both the Marconi supercomputer system at the Computational Simulation Centre and the Computer Center of St. Petersburg State University.
First principles calculations of the vibrational properties of single and dimer F-type centers in corundum crystals
The present paper investigates the F-type centers in α-Al2O3 through their electronic and vibrational properties from first principle calculations using a periodic supercell approach, a hybrid functional, and all-electron Gaussian basis sets as implemented in the CRYSTAL17 code. Single F-type and dimer F2-type centers related to oxygen vacancies in various charge states were considered. The defect-induced vibrational modes were identified and found to appear mainly in the low (up to 300 cm-1) and high (above 700 cm-1) frequency regions, depending on the defect charge. The perturbation introduced by the defects to the thermal nuclear motion in the crystal lattice is discussed in terms of ato…
Vibrational Analysis of Paraelectric–Ferroelectric Transition of LiNbO3: An Ab-Initio Quantum Mechanical Treatment
FSG acknowledges the CINECA award under the ISCRA initiative (HP10BJO47B) for the availability of high-performance computing resources and support.
Interstitial carbon defects in silicon. A quantum mechanical characterization through the infrared and Raman spectra.
The infrared (IR) and Raman spectra of eight substitutional carbon defects in silicon are computed at the quantum mechanical level by using a periodic supercell approach based on hybrid functionals, an all electron Gaussian type basis set and the CRYSTAL code. The single substitutional C s case and its combination with a vacancy (C s V and C s SiV) are considered first. The progressive saturation of the four bonds of a Si atom with C is then examined. The last set of defects consists of a chain of adjacent carbon atoms C s i , with i = 1-3. The simple substitutional case, C s , is the common first member of the three sets. All these defects show important, very characteristic features in th…
Substitutional carbon defects in silicon: A quantum mechanical characterization through the infrared and Raman spectra
EUROfusion Enabling Research Project, Grant/Award Number: ENR‐MFE19.ISSP‐UL‐02; GENCI, Grant/Award Number: 2018‐[A0050810537] (Ph. D'Arco) Access to the HPC resources of CINES/IDRIS/TGCC obtained thanks to the grant 2018-[A0050810537]
The VN2 negatively charged defect in diamond. A quantum mechanical investigation of the EPR response
Abstract The VN 2 − defect in diamond consists of a vacancy surrounded by two substitutional nitrogen atoms, which lower the local symmetry from Td to C2v. Calculations of the doublet ground state geometry, electronic structure, EPR parameters, and IR spectra of this defect are reported along with a preliminary investigation of the observed optical transition. For the most part our results were obtained using a uniform charge compensated supercell approach together with the B3LYP functional and all-electron Gaussian basis sets designed for the properties studied. In particular, the computed hyperfine and quadrupolar EPR parameters for the carbon and nitrogen atoms adjacent to the vacancy ag…
Ab initio simulations on charged interstitial oxygen migration in corundum
We have performed this work within the framework of the EUROfusion Consortium receiving funding from the European grant agreement 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. Authors thank R. Vila, A.I. Popov, A. Luchshik and R.A. Evarestov for fruitful discussions. To carry out large-scale calculations, we have used the HPC supercomputer at Stuttgart University (Germany)
Oxygen and vacancy defects in silicon. A quantum mechanical characterization through the IR and Raman spectra.
The Infrared (IR) and Raman spectra of various defects in silicon, containing both oxygen atoms (in the interstitial position, Oi) and a vacancy, are computed at the quantum mechanical level by using a periodic supercell approach based on a hybrid functional (B3LYP), an all-electron Gaussian-type basis set, and the Crystal code. The first of these defects is VO: the oxygen atom, twofold coordinated, saturates the unpaired electrons of two of the four carbon atoms on first neighbors of the vacancy. The two remaining unpaired electrons on the first neighbors of the vacancy can combine to give a triplet (Sz = 1) or a singlet (Sz = 0) state; both states are investigated for the neutral form of …
Ab initio simulations on migration paths of interstitial oxygen in corundum
Abstract Ionizing radiation produces in Al 2 O 3 (corundum) crystals primary Frenkel pairs of complementary defects (in oxygen sublattice these are oxygen vacancies and interstitial oxygen ions, V O − O i ). The interstitial O i atoms begin to migrate above certain temperature and create the dumbbell pairs with regular oxygen atoms (O reg − O i ). We have calculated the optimal dumbbell configurations and optimized further migration paths ( i.e. , O i interstitial can break the bond with one O reg atom and moves towards another, one of four next-neighbor O reg atoms). To simulate all possible O i migration trajectories, we have performed large-scale hybrid DFT-LCAO PBE0 calculations on 2 …
Nitrogen substitutional defects in silicon. A quantum mechanical investigation of the structural, electronic and vibrational properties
RD and FSG acknowledges the CINECA award (HP10CTG8YY) under the ISCRA initiative, for the availability of high performance computing resources and support.
Hybrid density functional calculations of hyperfine coupling tensor for hole-type defects in MgAl2O4
This work 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 application”. The views and opinions expressed herein do not necessarily reflect those of the European Commission.