Roberts Eglitis | University of Latvia (original) (raw)

Papers by Roberts Eglitis

Research paper thumbnail of Review of Systematic Tendencies in (001), (011) and (111) Surfaces Using B3PW as Well as B3LYP Computations of BaTiO3, CaTiO3, PbTiO3, SrTiO3, BaZrO3, CaZrO3, PbZrO3 and SrZrO3 Perovskites

Research paper thumbnail of Theoretical Study on (n,n)-Nanotubes Rolled-up from B/N Substituted Me-Graphene

Crystals

In this work, the n,n-type nanotube systems rolled up from the B/N substituted Me-graphene (i.e.,... more In this work, the n,n-type nanotube systems rolled up from the B/N substituted Me-graphene (i.e., Me-CBNT and Me-CNN, respectively) were investigated with the aid of the density functional theory (DFT). Due to the lattice dynamic instabilities until n=10, the n,0 and n,m nanotube systems were not involved in this study. According to our calculations at the Perdew-Burke-Ernzerhof (PBE) level, the n,n Me-CBNT and Me-CNNT systems possess excellent mechanical strengths. The Young’s moduli of Me-CBNTs can reach 60% of single-walled carbon nanotubes (SWCNTs), while their mass densities are only around 70% of SWCNTs. Based on the fully relaxed geometric configurations at the PBE level, the electronic configurations of the related nanotubes were evaluated by using the global hybrid functional B3LYP with 36% Fock exchanges. The n,n Me-CBNTs are metallic, while the n,n Me-CNNTs are semiconductors with the inherent band gaps in the range of 3.08 eV to 3.31 eV. The Bloch flat bands appear on bo...

Research paper thumbnail of Review of Systematic Tendencies in (001), (011) and (111) Surfaces Using B3PW as Well as B3LYP Computations of BaTiO 3 , CaTiO 3 , PbTiO 3 , SrTiO 3 , BaZrO 3 , CaZrO 3 , PbZrO 3 and SrZrO 3 Perovskites

Materials, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Enhancing photocatalytic overall water-splitting performance on dual-active-sites of the Co–P@MoS2 catalysts: a DFT study

Physical Chemistry Chemical Physics

Basal plane of Co–P@MoS2 was found to be prominently stabilized by Co–P band, and the synergy of ... more Basal plane of Co–P@MoS2 was found to be prominently stabilized by Co–P band, and the synergy of dual-active sites significantly improves OER and HER performance.

Research paper thumbnail of Overview of the Structural, Electronic and Optical Properties of the Cubic and Tetragonal Phases of PbTiO3 by Applying Hubbard Potential Correction

Materials

We have performed a systematic study resulting in detailed information on the structural, electro... more We have performed a systematic study resulting in detailed information on the structural, electronic and optical properties of the cubic (Pm3¯m) and tetragonal (P4mm) phases of PbTiO3 applying the GGA/PBE approximation with and without the Hubbard U potential correction. Through the variation in Hubbard potential values, we establish band gap predictions for the tetragonal phase of PbTiO3 that are in rather good agreement with experimental data. Furthermore, the bond lengths for both phases of PbTiO3 were assessed with experimental measurements, confirming the validity of our model, while chemical bond analysis highlights the covalent nature of the Ti–O and Pb–O bonds. In addition, the study of the optical properties of the two phases of PbTiO3, by applying Hubbard’ U potential, corrects the systematic inaccuracy of the GGA approximation, as well as validating the electronic analysis and offering excellent concordance with the experimental results. Therefore, our results underline t...

Research paper thumbnail of Review of First Principles Simulations of STO/BTO, STO/PTO, and SZO/PZO (001) Heterostructures

Crystals

In this study, we review our first-principles simulations for STO/BTO, STO/PTO, and SZO/PZO (001)... more In this study, we review our first-principles simulations for STO/BTO, STO/PTO, and SZO/PZO (001) heterostructures. Specifically, we report ab initio B3PW calculations for STO/BTO, STO/PTO, and SZO/PZO (001) interfaces, considering non-stoichiometric heterostructures in the process. Our ab initio B3PW calculations demonstrate that charge redistribution in the (001) interface region only subtly affects electronic structures. However, changes in stoichiometry result in significant shifts in band edges. The computed band gaps for the STO/BTO, STO/PTO, and SZO/PZO (001) interfaces are primarily determined according to whether the topmost layer of the augmented (001) film has an AO or BO2 termination. We predict an increase in the covalency of B-O bonds near the STO/BTO, STO/PTO, and SZO/PZO (001) heterostructures as compared to the BTO, PTO, and PZO bulk materials.

Research paper thumbnail of Ab Initio Computations of O and AO as well as ReO2, WO2 and BO2-Terminated ReO3, WO3, BaTiO3, SrTiO3 and BaZrO3 (001) Surfaces

Symmetry

We present and discuss the results of surface relaxation and rumpling computations for ReO3, WO3,... more We present and discuss the results of surface relaxation and rumpling computations for ReO3, WO3, SrTiO3, BaTiO3 and BaZrO3 (001) surfaces employing a hybrid B3LYP or B3PW description of exchange and correlation. In particular, we perform the first B3LYP computations for O-terminated ReO3 and WO3 (001) surfaces. In most cases, according to our B3LYP or B3PW computations for both surface terminations BO2- and O, AO-terminated ReO3, WO3, BaTiO3, SrTiO3 and BaZrO3 (001) surface upper layer atoms shift downwards, towards the bulk, the second layer atoms shift upwards and the third layer atoms, again, shift downwards. Our ab initio computes that ReO3, WO3, BaTiO3, SrTiO3 and BaZrO3 (001) surface Γ-Γ bandgaps are always smaller than their respective bulk Γ-Γ bandgaps. Our first principles compute that B-O atom chemical bond populations in the BaTiO3, SrTiO3 and BaZrO3 perovskite bulk are always smaller than near their BO2-terminated (001) surfaces. Just opposite, the Re-O and W-O chemical...

Research paper thumbnail of The adsorption behavior of phenol on the surface of 1D/2D M@MoS2 (M = Co and Rh) for hydrodeoxidation reaction: Insights from theoretical investigations

Research paper thumbnail of First-principles calculations of 0D/2D GQDs–MoS2 mixed van der Waals heterojunctions for photocatalysis: a transition from type I to type II

Physical Chemistry Chemical Physics, 2022

The type II band alignment of 0D/2D GQDs–MoS2 is realized by increasing the size of GQDs, benefic... more The type II band alignment of 0D/2D GQDs–MoS2 is realized by increasing the size of GQDs, beneficial to photocatalysis.

Research paper thumbnail of Effects of Electron Correlation inside Disordered Crystals

Crystals, 2022

We propose a novel approach for characterising the electron spectrum of disordered crystals const... more We propose a novel approach for characterising the electron spectrum of disordered crystals constructed from a Hamiltonian of electrons as well as phonons and a diagram approach for Green’s function. The system’s electronic states were modelled by means of the multi-band, tight-binding approach. The system’s Hamiltonian is described based on the electron wave functions at the field of the atom nucleus. Our novel approach incorporates the long-range Coulomb interplay of electrons located in different lattice positions. Explicit interpretations of Green’s functions are derived using a diagram method. Equations are obtained for the vertex components for the mass operators of the electron–electron as well aselectron–phonon interplays. A system of equations for the spectrum of elementary excitations in the crystal is obtained, in which the vertex components for the mass operators of electron–electron as well as electron–phonon interplays are renormalised. Thismakes it possible to perform...

Research paper thumbnail of Novel 2D boron nitride with optimal direct band gap: A theoretical prediction

Applied Surface Science, 2021

Research paper thumbnail of Ab initio calculations of ABO3 perovskite (001), (011) and (111) nano-surfaces, interfaces and defects

Modern Physics Letters B, 2020

We carried out ab initio calculations for technologically important ABO3 perovskite, such as, SrT... more We carried out ab initio calculations for technologically important ABO3 perovskite, such as, SrTiO3, BaTiO3, SrZrO3 and PbZrO3 (001), (011) and (111) nano-surfaces, interfaces and bulk [Formula: see text]-centers. For SrTiO3, BaTiO3, SrZrO3 and PbZrO3 (001) nano-surfaces, as a rule, all first surface layer atoms relax inward, whereas all second layer atoms relax outward, and, typically, all third surface layer atoms, again, relax inward. Calculated (001) surface energies for SrTiO3, BaTiO3, SrZrO3 and PbZrO3 perovskites are almost equal for both BO2 and AO-terminations, and always smaller than the (011) and (111) surface energies. We discussed the results of our ab initio calculations dealing with BaTiO3/SrTiO3 and SrZrO3/PbZrO3 (001) interfaces. We analyzed systematic trends in ABO3 perovskite bulk [Formula: see text]-center ab initio calculations.

Research paper thumbnail of First-Principles Simulation of Substitutional Defects in Perovskites

Defects and Surface-Induced Effects in Advanced Perovskites, 2000

The results of supercell calculations of electronic structure and related properties of substitut... more The results of supercell calculations of electronic structure and related properties of substitutional impurities in perovskite oxides KNbO3 and KTaO3 are discussed. For Fe impurities in KNbO3, the results obtained in the local density approximation (LDA) and in the LDA+U approach (that allows an ad hoc treatment of nonlocality in exchange-correlation) are compared, and different impurity charge configurations are discussed. The study of off-centre Li defects in incipient ferroelectric KTaO3 have been done by the appropriately parametrized Intermediate Neglect of Differential Overlap (INDO) method. The interaction energies of two off-centre impurities in different relative configurations are discussed.

Research paper thumbnail of Comparative Ab Initio Calculations of ReO3, SrZrO3, BaZrO3, PbZrO3 and CaZrO3 (001) Surfaces

Crystals, 2020

We performed, for first time, ab initio calculations for the ReO2-terminated ReO3 (001) surface a... more 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 chem...

Research paper thumbnail of Overview of the Structural, Electronic and Optical Properties of the Cubic and Tetragonal Phases of PbTiO3 by Applying Hubbard Potential Correction

Materials

We have performed a systematic study resulting in detailed information on the structural, electro... more We have performed a systematic study resulting in detailed information on the structural, electronic and optical properties of the cubic (Pm3¯m) and tetragonal (P4mm) phases of PbTiO3 applying the GGA/PBE approximation with and without the Hubbard U potential correction. Through the variation in Hubbard potential values, we establish band gap predictions for the tetragonal phase of PbTiO3 that are in rather good agreement with experimental data. Furthermore, the bond lengths for both phases of PbTiO3 were assessed with experimental measurements, confirming the validity of our model, while chemical bond analysis highlights the covalent nature of the Ti–O and Pb–O bonds. In addition, the study of the optical properties of the two phases of PbTiO3, by applying Hubbard’ U potential, corrects the systematic inaccuracy of the GGA approximation, as well as validating the electronic analysis and offering excellent concordance with the experimental results. Therefore, our results underline t...

Research paper thumbnail of Carbon nanotubes rolled from Me-graphene

Diamond and Related Materials

Research paper thumbnail of Computer Modeling of Point Defects, Impurity Self-Ordering Effects and Surfaces in Advanced Perovskite Ferroelectrics

Acta Physica Polonica A, 2000

The calculated optical properties of basic point defects-F-type centers and hole polarons-in KNbO... more The calculated optical properties of basic point defects-F-type centers and hole polarons-in KNbO 3 perovskite crystals are used for the interpretation of available experimental data. The results of quantum chemical calculations for perovskite KNb x Ta1x O 3 solid solutions are presented for x = 0, 0.125, 0.25, 0.75, and 1. An analysis of the optimized atomic and electronic structure clearly demonstrates that several nearest Nb atoms substituting for Ta in KTaO 3-unlike Ta impurities in KNbO3-reveal a self-ordering effect, which probably triggers the ferroelectricity observed in KNbxTa 1x O 3. Lastly, the (110) surface relaxations are calculated for SrTiO 3 and BaTiO 3 perovskites. The positions of atoms in 16 near-surface layers placed atop a slab of rigid ions are optimized using the classical shell model. Strong surface rumpling and surface-induced dipole moments perpendicular to the surface are predicted for both the O-terminated and Ti-terminated surfaces.

Research paper thumbnail of Metallic subnanometer porous silicon: A theoretical prediction

Physical Review B, 2021

In the present work, T-Si, a silicon-based counterpart of T-carbon, has been designed with the ai... more In the present work, T-Si, a silicon-based counterpart of T-carbon, has been designed with the aid of density functional theory (DFT) calculations. Its stability has been fully confirmed from energetic, mechanical, lattice dynamic, and thermodynamic aspects. Due to the space extrusion, the delocalized electrons on the Si 4 tetrahedrons are squeezed onto the inter-tetrahedron Si − Si bonds, which therefore leads T-Si to be metallic. Furthermore, the electronic conductivity of this new material has also been predicted and discussed in this work. This new silicon allotrope with a low density of 0.869 g/cm 3 can even floats on water. This designed ultralight form of Si paves the way for the applications in the fields of spacecraft and automobiles in the future.

Research paper thumbnail of Ab initio hybrid DFT calculations of BaTiO3 bulk and BaO-terminated (001) surface F-centers

International Journal of Modern Physics B, 2017

Using a supercell model and a hybrid B3PW exchange-correlation functional, we have performed firs... more Using a supercell model and a hybrid B3PW exchange-correlation functional, we have performed first principles calculations for the F-center in the BaTiO3 bulk and on the BaO-terminated (001) surface. We find that two Ti atoms nearest to the bulk F-center are repulsed, while nearest eight oxygen and four barium atoms relax toward the oxygen vacancy (by 1.06, 0.71 and 0.08% of the lattice constant [Formula: see text], respectively). The magnitudes of atomic displacements around the F-center located on the BaO-terminated (001) surface in most cases (except for Ti) are larger than those around the bulk F-center (0.1, 1.4 and 1.0% of [Formula: see text], respectively). Our calculated BaTiO3 bulk [Formula: see text]–[Formula: see text] bandgap of 3.55 eV is in an acceptable agreement with the respective experimental bandgap value of 3.2 eV. The pristine BaO-terminated (001) surface [Formula: see text]–[Formula: see text] bandgap (3.49 eV) is reduced with respect to the bulk bandgap value....

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

Computational Condensed Matter, 2016

Using a supercell model and B3PW hybrid exchange-correlation functional in the framework of the d... more 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 SrZrO 3 bulk and on the ZrO 2-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 SrZrO 3 bulk optical band gap (5.00 eV) is in a fair agreement with the experimental value of 5.6 eV. The ZrO 2-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 SrZrO 3 , calculated using 3 Â 3 Â 3 and 3 Â 3 Â 1 times expanded supercells, are located 1.12 and 0.93 eV under the conduction band bottom. The O vacancy in the SrZrO 3 bulk attracts 1.25e, and even less, only 1.10e on the ZrO 2terminated (001) surface. Performed calculations reveal significant enhancement of the chemical bond covalency among the SrZrO 3 bulk F-center and its nearest Zr atoms of 0.244e in comparison with the ideal SrZrO 3 perovskite ZreO chemical bond covalency of 0.100e. Our detected defect formation energy for the F-center located on the ZrO 2-terminated (001) surface 7.52 eV is somewhat smaller than in the SrZrO 3 bulk 7.55 eV. Our calculated formation energy difference may trigger the segregation of the Fcenter from the SrZrO 3 bulk towards the ZrO 2-terminated (001) surface.

Research paper thumbnail of Review of Systematic Tendencies in (001), (011) and (111) Surfaces Using B3PW as Well as B3LYP Computations of BaTiO3, CaTiO3, PbTiO3, SrTiO3, BaZrO3, CaZrO3, PbZrO3 and SrZrO3 Perovskites

Research paper thumbnail of Theoretical Study on (n,n)-Nanotubes Rolled-up from B/N Substituted Me-Graphene

Crystals

In this work, the n,n-type nanotube systems rolled up from the B/N substituted Me-graphene (i.e.,... more In this work, the n,n-type nanotube systems rolled up from the B/N substituted Me-graphene (i.e., Me-CBNT and Me-CNN, respectively) were investigated with the aid of the density functional theory (DFT). Due to the lattice dynamic instabilities until n=10, the n,0 and n,m nanotube systems were not involved in this study. According to our calculations at the Perdew-Burke-Ernzerhof (PBE) level, the n,n Me-CBNT and Me-CNNT systems possess excellent mechanical strengths. The Young’s moduli of Me-CBNTs can reach 60% of single-walled carbon nanotubes (SWCNTs), while their mass densities are only around 70% of SWCNTs. Based on the fully relaxed geometric configurations at the PBE level, the electronic configurations of the related nanotubes were evaluated by using the global hybrid functional B3LYP with 36% Fock exchanges. The n,n Me-CBNTs are metallic, while the n,n Me-CNNTs are semiconductors with the inherent band gaps in the range of 3.08 eV to 3.31 eV. The Bloch flat bands appear on bo...

Research paper thumbnail of Review of Systematic Tendencies in (001), (011) and (111) Surfaces Using B3PW as Well as B3LYP Computations of BaTiO 3 , CaTiO 3 , PbTiO 3 , SrTiO 3 , BaZrO 3 , CaZrO 3 , PbZrO 3 and SrZrO 3 Perovskites

Materials, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Enhancing photocatalytic overall water-splitting performance on dual-active-sites of the Co–P@MoS2 catalysts: a DFT study

Physical Chemistry Chemical Physics

Basal plane of Co–P@MoS2 was found to be prominently stabilized by Co–P band, and the synergy of ... more Basal plane of Co–P@MoS2 was found to be prominently stabilized by Co–P band, and the synergy of dual-active sites significantly improves OER and HER performance.

Research paper thumbnail of Overview of the Structural, Electronic and Optical Properties of the Cubic and Tetragonal Phases of PbTiO3 by Applying Hubbard Potential Correction

Materials

We have performed a systematic study resulting in detailed information on the structural, electro... more We have performed a systematic study resulting in detailed information on the structural, electronic and optical properties of the cubic (Pm3¯m) and tetragonal (P4mm) phases of PbTiO3 applying the GGA/PBE approximation with and without the Hubbard U potential correction. Through the variation in Hubbard potential values, we establish band gap predictions for the tetragonal phase of PbTiO3 that are in rather good agreement with experimental data. Furthermore, the bond lengths for both phases of PbTiO3 were assessed with experimental measurements, confirming the validity of our model, while chemical bond analysis highlights the covalent nature of the Ti–O and Pb–O bonds. In addition, the study of the optical properties of the two phases of PbTiO3, by applying Hubbard’ U potential, corrects the systematic inaccuracy of the GGA approximation, as well as validating the electronic analysis and offering excellent concordance with the experimental results. Therefore, our results underline t...

Research paper thumbnail of Review of First Principles Simulations of STO/BTO, STO/PTO, and SZO/PZO (001) Heterostructures

Crystals

In this study, we review our first-principles simulations for STO/BTO, STO/PTO, and SZO/PZO (001)... more In this study, we review our first-principles simulations for STO/BTO, STO/PTO, and SZO/PZO (001) heterostructures. Specifically, we report ab initio B3PW calculations for STO/BTO, STO/PTO, and SZO/PZO (001) interfaces, considering non-stoichiometric heterostructures in the process. Our ab initio B3PW calculations demonstrate that charge redistribution in the (001) interface region only subtly affects electronic structures. However, changes in stoichiometry result in significant shifts in band edges. The computed band gaps for the STO/BTO, STO/PTO, and SZO/PZO (001) interfaces are primarily determined according to whether the topmost layer of the augmented (001) film has an AO or BO2 termination. We predict an increase in the covalency of B-O bonds near the STO/BTO, STO/PTO, and SZO/PZO (001) heterostructures as compared to the BTO, PTO, and PZO bulk materials.

Research paper thumbnail of Ab Initio Computations of O and AO as well as ReO2, WO2 and BO2-Terminated ReO3, WO3, BaTiO3, SrTiO3 and BaZrO3 (001) Surfaces

Symmetry

We present and discuss the results of surface relaxation and rumpling computations for ReO3, WO3,... more We present and discuss the results of surface relaxation and rumpling computations for ReO3, WO3, SrTiO3, BaTiO3 and BaZrO3 (001) surfaces employing a hybrid B3LYP or B3PW description of exchange and correlation. In particular, we perform the first B3LYP computations for O-terminated ReO3 and WO3 (001) surfaces. In most cases, according to our B3LYP or B3PW computations for both surface terminations BO2- and O, AO-terminated ReO3, WO3, BaTiO3, SrTiO3 and BaZrO3 (001) surface upper layer atoms shift downwards, towards the bulk, the second layer atoms shift upwards and the third layer atoms, again, shift downwards. Our ab initio computes that ReO3, WO3, BaTiO3, SrTiO3 and BaZrO3 (001) surface Γ-Γ bandgaps are always smaller than their respective bulk Γ-Γ bandgaps. Our first principles compute that B-O atom chemical bond populations in the BaTiO3, SrTiO3 and BaZrO3 perovskite bulk are always smaller than near their BO2-terminated (001) surfaces. Just opposite, the Re-O and W-O chemical...

Research paper thumbnail of The adsorption behavior of phenol on the surface of 1D/2D M@MoS2 (M = Co and Rh) for hydrodeoxidation reaction: Insights from theoretical investigations

Research paper thumbnail of First-principles calculations of 0D/2D GQDs–MoS2 mixed van der Waals heterojunctions for photocatalysis: a transition from type I to type II

Physical Chemistry Chemical Physics, 2022

The type II band alignment of 0D/2D GQDs–MoS2 is realized by increasing the size of GQDs, benefic... more The type II band alignment of 0D/2D GQDs–MoS2 is realized by increasing the size of GQDs, beneficial to photocatalysis.

Research paper thumbnail of Effects of Electron Correlation inside Disordered Crystals

Crystals, 2022

We propose a novel approach for characterising the electron spectrum of disordered crystals const... more We propose a novel approach for characterising the electron spectrum of disordered crystals constructed from a Hamiltonian of electrons as well as phonons and a diagram approach for Green’s function. The system’s electronic states were modelled by means of the multi-band, tight-binding approach. The system’s Hamiltonian is described based on the electron wave functions at the field of the atom nucleus. Our novel approach incorporates the long-range Coulomb interplay of electrons located in different lattice positions. Explicit interpretations of Green’s functions are derived using a diagram method. Equations are obtained for the vertex components for the mass operators of the electron–electron as well aselectron–phonon interplays. A system of equations for the spectrum of elementary excitations in the crystal is obtained, in which the vertex components for the mass operators of electron–electron as well as electron–phonon interplays are renormalised. Thismakes it possible to perform...

Research paper thumbnail of Novel 2D boron nitride with optimal direct band gap: A theoretical prediction

Applied Surface Science, 2021

Research paper thumbnail of Ab initio calculations of ABO3 perovskite (001), (011) and (111) nano-surfaces, interfaces and defects

Modern Physics Letters B, 2020

We carried out ab initio calculations for technologically important ABO3 perovskite, such as, SrT... more We carried out ab initio calculations for technologically important ABO3 perovskite, such as, SrTiO3, BaTiO3, SrZrO3 and PbZrO3 (001), (011) and (111) nano-surfaces, interfaces and bulk [Formula: see text]-centers. For SrTiO3, BaTiO3, SrZrO3 and PbZrO3 (001) nano-surfaces, as a rule, all first surface layer atoms relax inward, whereas all second layer atoms relax outward, and, typically, all third surface layer atoms, again, relax inward. Calculated (001) surface energies for SrTiO3, BaTiO3, SrZrO3 and PbZrO3 perovskites are almost equal for both BO2 and AO-terminations, and always smaller than the (011) and (111) surface energies. We discussed the results of our ab initio calculations dealing with BaTiO3/SrTiO3 and SrZrO3/PbZrO3 (001) interfaces. We analyzed systematic trends in ABO3 perovskite bulk [Formula: see text]-center ab initio calculations.

Research paper thumbnail of First-Principles Simulation of Substitutional Defects in Perovskites

Defects and Surface-Induced Effects in Advanced Perovskites, 2000

The results of supercell calculations of electronic structure and related properties of substitut... more The results of supercell calculations of electronic structure and related properties of substitutional impurities in perovskite oxides KNbO3 and KTaO3 are discussed. For Fe impurities in KNbO3, the results obtained in the local density approximation (LDA) and in the LDA+U approach (that allows an ad hoc treatment of nonlocality in exchange-correlation) are compared, and different impurity charge configurations are discussed. The study of off-centre Li defects in incipient ferroelectric KTaO3 have been done by the appropriately parametrized Intermediate Neglect of Differential Overlap (INDO) method. The interaction energies of two off-centre impurities in different relative configurations are discussed.

Research paper thumbnail of Comparative Ab Initio Calculations of ReO3, SrZrO3, BaZrO3, PbZrO3 and CaZrO3 (001) Surfaces

Crystals, 2020

We performed, for first time, ab initio calculations for the ReO2-terminated ReO3 (001) surface a... more 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 chem...

Research paper thumbnail of Overview of the Structural, Electronic and Optical Properties of the Cubic and Tetragonal Phases of PbTiO3 by Applying Hubbard Potential Correction

Materials

We have performed a systematic study resulting in detailed information on the structural, electro... more We have performed a systematic study resulting in detailed information on the structural, electronic and optical properties of the cubic (Pm3¯m) and tetragonal (P4mm) phases of PbTiO3 applying the GGA/PBE approximation with and without the Hubbard U potential correction. Through the variation in Hubbard potential values, we establish band gap predictions for the tetragonal phase of PbTiO3 that are in rather good agreement with experimental data. Furthermore, the bond lengths for both phases of PbTiO3 were assessed with experimental measurements, confirming the validity of our model, while chemical bond analysis highlights the covalent nature of the Ti–O and Pb–O bonds. In addition, the study of the optical properties of the two phases of PbTiO3, by applying Hubbard’ U potential, corrects the systematic inaccuracy of the GGA approximation, as well as validating the electronic analysis and offering excellent concordance with the experimental results. Therefore, our results underline t...

Research paper thumbnail of Carbon nanotubes rolled from Me-graphene

Diamond and Related Materials

Research paper thumbnail of Computer Modeling of Point Defects, Impurity Self-Ordering Effects and Surfaces in Advanced Perovskite Ferroelectrics

Acta Physica Polonica A, 2000

The calculated optical properties of basic point defects-F-type centers and hole polarons-in KNbO... more The calculated optical properties of basic point defects-F-type centers and hole polarons-in KNbO 3 perovskite crystals are used for the interpretation of available experimental data. The results of quantum chemical calculations for perovskite KNb x Ta1x O 3 solid solutions are presented for x = 0, 0.125, 0.25, 0.75, and 1. An analysis of the optimized atomic and electronic structure clearly demonstrates that several nearest Nb atoms substituting for Ta in KTaO 3-unlike Ta impurities in KNbO3-reveal a self-ordering effect, which probably triggers the ferroelectricity observed in KNbxTa 1x O 3. Lastly, the (110) surface relaxations are calculated for SrTiO 3 and BaTiO 3 perovskites. The positions of atoms in 16 near-surface layers placed atop a slab of rigid ions are optimized using the classical shell model. Strong surface rumpling and surface-induced dipole moments perpendicular to the surface are predicted for both the O-terminated and Ti-terminated surfaces.

Research paper thumbnail of Metallic subnanometer porous silicon: A theoretical prediction

Physical Review B, 2021

In the present work, T-Si, a silicon-based counterpart of T-carbon, has been designed with the ai... more In the present work, T-Si, a silicon-based counterpart of T-carbon, has been designed with the aid of density functional theory (DFT) calculations. Its stability has been fully confirmed from energetic, mechanical, lattice dynamic, and thermodynamic aspects. Due to the space extrusion, the delocalized electrons on the Si 4 tetrahedrons are squeezed onto the inter-tetrahedron Si − Si bonds, which therefore leads T-Si to be metallic. Furthermore, the electronic conductivity of this new material has also been predicted and discussed in this work. This new silicon allotrope with a low density of 0.869 g/cm 3 can even floats on water. This designed ultralight form of Si paves the way for the applications in the fields of spacecraft and automobiles in the future.

Research paper thumbnail of Ab initio hybrid DFT calculations of BaTiO3 bulk and BaO-terminated (001) surface F-centers

International Journal of Modern Physics B, 2017

Using a supercell model and a hybrid B3PW exchange-correlation functional, we have performed firs... more Using a supercell model and a hybrid B3PW exchange-correlation functional, we have performed first principles calculations for the F-center in the BaTiO3 bulk and on the BaO-terminated (001) surface. We find that two Ti atoms nearest to the bulk F-center are repulsed, while nearest eight oxygen and four barium atoms relax toward the oxygen vacancy (by 1.06, 0.71 and 0.08% of the lattice constant [Formula: see text], respectively). The magnitudes of atomic displacements around the F-center located on the BaO-terminated (001) surface in most cases (except for Ti) are larger than those around the bulk F-center (0.1, 1.4 and 1.0% of [Formula: see text], respectively). Our calculated BaTiO3 bulk [Formula: see text]–[Formula: see text] bandgap of 3.55 eV is in an acceptable agreement with the respective experimental bandgap value of 3.2 eV. The pristine BaO-terminated (001) surface [Formula: see text]–[Formula: see text] bandgap (3.49 eV) is reduced with respect to the bulk bandgap value....

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

Computational Condensed Matter, 2016

Using a supercell model and B3PW hybrid exchange-correlation functional in the framework of the d... more 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 SrZrO 3 bulk and on the ZrO 2-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 SrZrO 3 bulk optical band gap (5.00 eV) is in a fair agreement with the experimental value of 5.6 eV. The ZrO 2-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 SrZrO 3 , calculated using 3 Â 3 Â 3 and 3 Â 3 Â 1 times expanded supercells, are located 1.12 and 0.93 eV under the conduction band bottom. The O vacancy in the SrZrO 3 bulk attracts 1.25e, and even less, only 1.10e on the ZrO 2terminated (001) surface. Performed calculations reveal significant enhancement of the chemical bond covalency among the SrZrO 3 bulk F-center and its nearest Zr atoms of 0.244e in comparison with the ideal SrZrO 3 perovskite ZreO chemical bond covalency of 0.100e. Our detected defect formation energy for the F-center located on the ZrO 2-terminated (001) surface 7.52 eV is somewhat smaller than in the SrZrO 3 bulk 7.55 eV. Our calculated formation energy difference may trigger the segregation of the Fcenter from the SrZrO 3 bulk towards the ZrO 2-terminated (001) surface.