scholarly journals Chern and Z2 topological insulating phases in perovskite-derived 4d and 5d oxide buckled honeycomb lattices

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Okan Köksal ◽  
Rossitza Pentcheva
Keyword(s):  
Lattice Constant ◽  
Density Functional ◽  
Strong Dependence ◽  
Density Functional Theory Calculations ◽  
Coulomb Repulsion ◽  
Band Gaps ◽  
Edge States ◽  
Topological Properties ◽  
Gap Opening ◽  
A Site

AbstractBased on density functional theory calculations including a Coulomb repulsion parameter U, we explore the topological properties of (LaXO3)2/(LaAlO3)4 (111) with X = 4d and 5d cations. The metastable ferromagnetic phases of LaTcO3 and LaPtO3 with preserved P321 symmetry emerge as Chern insulators (CI) with C = 2 and 1 and band gaps of 41 and 38 meV at the lateral lattice constant of LaAlO3, respectively. Berry curvatures, spin textures as well as edge states provide additional insight into the nature of the CI states. While for X = Tc the CI phase is further stabilized under tensile strain, for X = Pd and Pt a site disproportionation takes place when increasing the lateral lattice constant from aLAO to aLNO. The CI phase of X = Pt shows a strong dependence on the Hubbard U parameter with sign reversal for higher values associated with the change of band gap opening mechanism. Parallels to the previously studied (X2O3)1/(Al2O3)5 (0001) honeycomb corundum layers are discussed. Additionally, non-magnetic systems with X = Mo and W are identified as potential candidates for Z2 topological insulators at aLAO with band gaps of 26 and 60 meV, respectively. The computed edge states and Z2 invariants underpin the non-trivial topological properties.

A computational study of hydrogen doping induced metal-to-insulator transition in CaFeO3, SrFeO3, BaFeO3 and SmMnO3

2019 ◽  
Vol 21 (45) ◽  
pp. 25397-25405
Author(s):  
Shukai Yao ◽  
Pilsun Yoo ◽  
Peilin Liao
Keyword(s):  
Density Functional Theory ◽  
Transition Metal ◽  
First Principles ◽  
Density Functional ◽  
Computational Study ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Hydrogen Doping ◽  
Gap Opening ◽  
Metal To Insulator Transition

First principles density functional theory calculations were performed to identify transition metal perovskites CaFeO3, SrFeO3, BaFeO3 and SmMnO3 as promising candidates with large band gap opening upon hydrogen doping.

Graphene-Based Sensors for Monitoring Strain

2013 ◽  
Vol 3 (1) ◽  
pp. 74-83
Author(s):  
M. Mirnezhad ◽  
R. Ansari ◽  
H. Rouhi ◽  
M. Faghihnasiri
Keyword(s):  
Fermi Level ◽  
Band Gap ◽  
Strain Distribution ◽  
Density Functional ◽  
Tight Binding ◽  
Density Functional Theory Calculations ◽  
Generalized Gradient ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Gap Opening

The application of graphene as a nanosensor in measuring strain through its band structure around the Fermi level is investigated in this paper. The mechanical properties of graphene as well as its electronic structure are determined by using the density functional theory calculations within the framework of generalized gradient approximation. In the case of electronic properties, the simulations are applied for symmetrical and asymmetrical strain distributions in elastic range; also the tight-binding approach is implemented to verify the results. It is indicated that the energy band gap does not change with the symmetrical strain distribution but depend on the asymmetric strain distribution, increasing strain leads to band gap opening around the Fermi level.

scholarly journals Layer-dependent topological phase in a two-dimensional quasicrystal and approximant

2020 ◽  
Vol 117 (42) ◽  
pp. 26135-26140
Author(s):  
Jeffrey D. Cain ◽  
Amin Azizi ◽  
Matthias Conrad ◽  
Sinéad M. Griffin ◽  
Alex Zettl
Keyword(s):  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Transition Metal Dichalcogenide ◽  
Material System ◽  
Two Dimensional ◽  
Topological Properties ◽  
Scanning Transmission ◽  
Layered Transition Metal ◽  
Low Dimensional ◽  
Physical Phenomena

The electronic and topological properties of materials are derived from the interplay between crystalline symmetry and dimensionality. Simultaneously introducing “forbidden” symmetries via quasiperiodic ordering with low dimensionality into a material system promises the emergence of new physical phenomena. Here, we isolate a two-dimensional (2D) chalcogenide quasicrystal and approximant, and investigate their electronic and topological properties. The 2D layers of the materials with a composition close to Ta1.6Te, derived from a layered transition metal dichalcogenide, are isolated with standard exfoliation techniques, and investigated with electron diffraction and atomic resolution scanning transmission electron microscopy. Density functional theory calculations and symmetry analysis of the large unit cell crystalline approximant of the quasicrystal, Ta21Te13, reveal the presence of symmetry-protected nodal crossings in the quasicrystalline and approximant phases, whose presence is tunable by layer number. Our study provides a platform for the exploration of physics in quasicrystalline, low-dimensional materials and the interconnected nature of topology, dimensionality, and symmetry in electronic systems.

Magnetic Properties of YBa2Cu3O6 Studied by Density Functional Theory Calculations

2019 ◽  
Vol 966 ◽  
pp. 257-262 ◽  
Author(s):  
Irwan Ramli ◽  
S.S Mohd-Tajudin ◽  
Muhammad Redo Ramadhan ◽  
Dita Puspita Sari ◽  
Shukri Sulaiman ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Magnetic Properties ◽  
Density Functional ◽  
Strong Dependence ◽  
Density Functional Theory Calculations ◽  
Internal Field ◽  
Experimental Result ◽  
Functional Theory ◽  
Calculation Technique ◽  
U Value

We present the results of investigations on the muon sitesin YBa2Cu3O6(YBCO6) by using the density functional theory (DFT) calculation technique in order to achieve a deeper understanding of its magnetic properties. We included the Hubbard parameter, U, among electrons in our DFT calculations in order to simulate realistic electronic and magnetic state in YBCO6. We found that the U value does not affect the muon sites in YBCO6but the related internal field has strong dependence on U value. In this study, we tried to optimize the value of Ucomparing with the experimental result.

scholarly journals Extensive Benchmarking of DFT+U Calculations for Predicting Band Gaps

2021 ◽  
Vol 11 (5) ◽  
pp. 2395 ◽  
Author(s):  
Nicole E. Kirchner-Hall ◽  
Wayne Zhao ◽  
Yihuang Xiong ◽  
Iurii Timrov ◽  
Ismaila Dabo
Keyword(s):  
Total Energy ◽  
Band Gap ◽  
Density Functional ◽  
Practical Importance ◽  
Computational Cost ◽  
Potential Method ◽  
Band Gaps ◽  
Edge States ◽  
Piecewise Linearity ◽  
Hubbard U

Accurate computational predictions of band gaps are of practical importance to the modeling and development of semiconductor technologies, such as (opto)electronic devices and photoelectrochemical cells. Among available electronic-structure methods, density-functional theory (DFT) with the Hubbard U correction (DFT+U) applied to band edge states is a computationally tractable approach to improve the accuracy of band gap predictions beyond that of DFT calculations based on (semi)local functionals. At variance with DFT approximations, which are not intended to describe optical band gaps and other excited-state properties, DFT+U can be interpreted as an approximate spectral-potential method when U is determined by imposing the piecewise linearity of the total energy with respect to electronic occupations in the Hubbard manifold (thus removing self-interaction errors in this subspace), thereby providing a (heuristic) justification for using DFT+U to predict band gaps. However, it is still frequent in the literature to determine the Hubbard U parameters semiempirically by tuning their values to reproduce experimental band gaps, which ultimately alters the description of other total-energy characteristics. Here, we present an extensive assessment of DFT+U band gaps computed using self-consistent ab initio U parameters obtained from density-functional perturbation theory to impose the aforementioned piecewise linearity of the total energy. The study is carried out on 20 compounds containing transition-metal or p-block (group III-IV) elements, including oxides, nitrides, sulfides, oxynitrides, and oxysulfides. By comparing DFT+U results obtained using nonorthogonalized and orthogonalized atomic orbitals as Hubbard projectors, we find that the predicted band gaps are extremely sensitive to the type of projector functions and that the orthogonalized projectors give the most accurate band gaps, in satisfactory agreement with experimental data. This work demonstrates that DFT+U may serve as a useful method for high-throughput workflows that require reliable band gap predictions at moderate computational cost.

scholarly journals Controlling Multiple Orderings in Metal Thiocyanate Molecular Perovskites Ax{Ni[Bi(SCN)6]}

2020 ◽  
Author(s):  
Jie Yie Lee ◽  
Sanliang Ling ◽  
Stephen Argent ◽  
Mark Senn ◽  
Laura Cañadillas-Delgado ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Double Perovskites ◽  
Functional Theory ◽  
X Ray ◽  
Vacancy Ordering ◽  
A Site ◽  
Symmetry Mode ◽  
Site Vacancy

<p>We report four new A-site vacancy ordered thiocyanate double double perovskites,</p><p>A1􀀀xfNi[Bi(SCN)6]1􀀀x3 }, A = K<sup>+</sup>, NH4<sup>+</sup>, CH3(NH3)<sup>+</sup> (MeNH<sub>3</sub><sup>+</sup>) and C(NH<sub>2</sub>)<sub>3</sub><sup>+</sup> (Gua<sup>+</sup>), including the first examples of thiocyanate perovskites containing organic A-site cations. We show, using a combination of X-ray and neutron diffraction, that the structure of these frameworks depends on the A-site cation, and that these frameworks possess complex vacancy-ordering patterns and cooperative octahedral tilts distinctly different from atomic perovskites. Density functional theory calculations uncover the energetic origin of these complex orders and allow us to propose a simple rule to predict favoured A-site cation orderings for a given tilt sequence. We use these insights, in combination with symmetry mode analyses, to show that these complex orders offer a new route to non-centrosymmetric perovskites which render them as excellent candidates for</p><p>piezo- and ferroelectric applications.</p>

scholarly journals Effects of reduced dimensionality on the electronic structure and defect chemistry of semiconducting hybrid organic–inorganic PbS solids

2011 ◽  
Vol 467 (2131) ◽  
pp. 1970-1985 ◽  
Author(s):  
Aron Walsh
Keyword(s):  
Density Functional ◽  
Defect Formation ◽  
Metal Organic Framework ◽  
Three Dimensional ◽  
Density Functional Theory Calculations ◽  
Substantial Contribution ◽  
Intrinsic Defect ◽  
Edge States ◽  
Electronic Effects ◽  
Reduced Dimensionality

The combination of inorganic and organic frameworks to produce crystalline hybrid semiconductors offers a pathway for obtaining novel photovoltaic and optoelectronic materials. Taking an archetypal binary semiconductor, PbS (galena), we investigate the electronic effects of the reduced dimensionality in the PbS framework on transition from bulk PbS to three-dimensional and one-dimensional hybrid inorganic–organic networks. Analysis of density functional theory calculations reveals the substantial contribution of the organic (benzenehexathiol derivates) to the band-edge states. Implications for intrinsic defect formation and potential application in solar cell devices are discussed, as well as future design pathways for engineering the electronic properties of this new class of hybrid metal–organic framework.

Contrasting 1D tunnel-structured and 2D layered polymorphs of V2O5: relating crystal structure and bonding to band gaps and electronic structure

2016 ◽  
Vol 18 (23) ◽  
pp. 15798-15806 ◽  
Author(s):  
Thomas M. Tolhurst ◽  
Brett Leedahl ◽  
Justin L. Andrews ◽  
Peter M. Marley ◽  
Sarbajit Banerjee ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Density Functional Theory ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Band Gaps ◽  
Structure Property ◽  
Functional Theory ◽  
X Ray ◽  
Structure Property Relationships ◽  
Structure And Bonding

An elucidation of structure–property relationships in V2O5 polymorphs using synchrotron X-ray spectroscopy and density functional theory calculations.

scholarly journals A band-gap database for semiconducting inorganic materials calculated with hybrid functional

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Sangtae Kim ◽  
Miso Lee ◽  
Changho Hong ◽  
Youngchae Yoon ◽  
Hyungmin An ◽  
...  
Keyword(s):  
Band Gap ◽  
Density Functional ◽  
Magnetic Ordering ◽  
Density Functional Theory Calculations ◽  
Inorganic Materials ◽  
Band Gaps ◽  
Device Performance ◽  
Photovoltaic Devices ◽  
Hybrid Functional ◽  
Functional Theory

Abstract Semiconducting inorganic materials with band gaps ranging between 0 and 5 eV constitute major components in electronic, optoelectronic and photovoltaic devices. Since the band gap is a primary material property that affects the device performance, large band-gap databases are useful in selecting optimal materials in each application. While there exist several band-gap databases that are theoretically compiled by density-functional-theory calculations, they suffer from computational limitations such as band-gap underestimation and metastable magnetism. In this data descriptor, we present a computational database of band gaps for 10,481 materials compiled by applying a hybrid functional and considering the stable magnetic ordering. For benchmark materials, the root-mean-square error in reference to experimental data is 0.36 eV, significantly smaller than 0.75–1.05 eV in the existing databases. Furthermore, we identify many small-gap materials that are misclassified as metals in other databases. By providing accurate band gaps, the present database will be useful in screening materials in diverse applications.

scholarly journals Structural and electronic properties of oligo- and polythiophenes modified by substituents

2012 ◽  
Vol 3 ◽  
pp. 909-919 ◽  
Author(s):  
Simon P Rittmeyer ◽  
Axel Groß
Keyword(s):  
Electronic Properties ◽  
Density Functional ◽  
Electronic Devices ◽  
Density Functional Theory Calculations ◽  
Building Blocks ◽  
Band Gaps ◽  
Molecular Electronic ◽  
Functional Theory ◽  
Structural And Electronic Properties ◽  
Electronic And Structural Properties

The electronic and structural properties of oligo- and polythiophenes that can be used as building blocks for molecular electronic devices have been studied by using periodic density functional theory calculations. We have in particular focused on the effect of substituents on the electronic structure of thiophenes. Whereas singly bonded substituents, such as methyl, amino or nitro groups, change the electronic properties of thiophene monomers and dimers, they hardly influence the band gap of polythiophene. In contrast, phenyl-substituted polythiophenes as well as vinyl-bridged polythiophene derivatives exhibit drastically modified band gaps. These effects cannot be explained by simple electron removal or addition, as calculations for charged polythiophenes demonstrate.

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