scholarly journals Strain Induced Topological Insulator Phase in CsPbBrxI3−x (x = 0, 1, 2, and 3) Perovskite: A Theoretical Study

2021 ◽  
Vol 11 (12) ◽  
pp. 5353
Author(s):  
Jen-Chuan Tung ◽  
Yu-Hsuan Hsieh ◽  
Po-Liang Liu
Keyword(s):  
Band Gap ◽  
Topological Insulator ◽  
Density Functional ◽  
Iodine Concentration ◽  
Electric Polarization ◽  
Small Displacement ◽  
Surface Band ◽  
Lattice Constants ◽  
Symmetric Point ◽  
Conduction Bands

First-principles density functional theory was used to determine the surface band structures of CsPbBrxI3−x (x = 0, 1, 2, and 3) perovskites. The equilibrium lattice constants of CsPbBrxI3−x were obtained from the minimum of the total energy as a function of the iodine concentration. We discovered that the band gaps of CsPbBrxI3−x decreased monotonically under pressure. The phase change from a normal insulator to a topological insulator was found at approximately 2–4 GPa. The Pbp- and Brs-orbitals inverted at the R symmetric point with and without spin–orbit coupling. Nontrivial Z2 topological numbers were obtained, and the surface conduction bands were demonstrated theoretically using a 1 × 1 × 10 supercell. We ascertained that CsPbBr2I has the largest electric polarization 0.025 C/m2 under a compression strain of 10%. We also observed that in the normal insulation phase, the band gap increases with a small displacement of the central Pb atom in the z-direction, but in the topological insulator phase, the band gap decreases with the movement of the Pb atom in the z-direction. Additionally, in the supercell structure, CsPbBrxI3−x is a ferroelectric topological insulator because the Pb atom leaves its own equilibrium position.

scholarly journals Heavy Thallium Based Fluoroperovskite TlAF3 (A = Ge, Sn and Pb) Compounds: A Computational Investigation

2021 ◽  
Author(s):  
Shams U Zaman ◽  
Nasir Mehmood ◽  
Sajid Khan ◽  
Rashid Ahmad ◽  
Nadia Sultan ◽  
...  
Keyword(s):  
Density Functional ◽  
Effective Atomic Number ◽  
Full Potential ◽  
Generalized Gradient ◽  
Lattice Constants ◽  
Conduction Bands ◽  
The Density Functional Theory ◽  
Theoretical Investigations ◽  
First Time ◽  
Linearized Augmented Plane Wave

Abstract Combination of heavy elements in forming a stable system leads to enhancement in effective atomic number making it desirable in many applications such as detection and shielding of radiation. We present our theoretical investigations on new Thallium based heavy fluoroperovskites TlAF3 (A = Ge, Sn and Pb). The study is carried out to explore the structural, elastic, electronic, and optical properties through the Density Functional Theory (DFT) using the Full-Potential Linearized Augmented Plane Wave (FP-LAPW) method implemented in WIEN2k. Generalized Gradient Approximation with consideration of electronic correlation effects (GGA+U) was employed for calculations. The lattice constants deduced from the optimization curves were found to be in the range of 4.00 Å to 4.85 Å. Elastic properties were obtained from the calculated elastic constants. From band structure calculations, it is evident that the bandgaps range from 0.84 to 1.89 eV. All the studied compounds exhibit indirect bandgap nature. Fluorine atom contributes significant number of electronic states in valence and conduction bands of all studied compounds. The optical response in terms of refractive index, extinction coefficient, optical conductivity, reflectivity, and absorption coefficients are calculated and discussed in the energy range of (0-20) eV. The properties of compounds in this study are being reported for the first time.

scholarly journals Predicting the strain-mediated topological phase transition in 3D cubic ThTaN3

2018 ◽  
Vol 9 ◽  
pp. 1399-1404 ◽  
Author(s):  
Chunmei Zhang ◽  
Aijun Du
Keyword(s):  
Band Gap ◽  
Topological Insulator ◽  
Density Functional ◽  
Compressive Strain ◽  
Fermi Velocity ◽  
Spin Orbital ◽  
Functional Theory ◽  
Topological Phase Transition ◽  
Potential Applications ◽  
Spin Orbital Coupling

The cubic ThTaN3 compound has long been known as a semiconductor with a band gap of approximately 1 eV, but its electronic properties remain largely unexplored. By using density functional theory, we find that the band gap of ThTaN3 is very sensitive to the hydrostatic pressure/strain. A Dirac cone can emerge around the Γ point with an ultrahigh Fermi velocity at a compressive strain of 8%. Interestingly, the effect of spin–orbital coupling (SOC) is significant, leading to a band gap reduction of 0.26 eV in the ThTaN3 compound. Moreover, the strong SOC can turn ThTaN3 into a topological insulator with a large inverted gap up to 0.25 eV, which can be primarily attributed to the inversion between the d-orbital of the heavy element Ta and the p-orbital of N. Our results highlight a new 3D topological insulator with strain-mediated topological transition for potential applications in future spintronics.

scholarly journals Theoretical Calculations of Structural, Mechanical, Electronic And Optical Properties of Sn2S3 Under Pressure

2021 ◽  
Author(s):  
Baishu Chen ◽  
Wenxia Zhu ◽  
Chunxiang Wang ◽  
Chang Wang ◽  
Yuanzuo Li ◽  
...  
Keyword(s):  
Optical Properties ◽  
Band Gap ◽  
Density Functional ◽  
Mechanical Stability ◽  
Pressure Effect ◽  
Theoretical Calculations ◽  
Structural Parameters ◽  
Electronic And Optical Properties ◽  
Lattice Constants ◽  
The Density Functional Theory

Abstract The pressure effect on the structural, mechanical, electronic and optical properties of Sn2S3 in the pressure range of 0–35 GPa have been evaluated by means of the first-principles calculations based on the density-functional theory. The structural parameters of Sn2S3 at 0 GPa such as lattice constants and cell volumes are consistent with the previous theoretical and experiment reports. The mechanical properties about the elastic constants (Cij) and polycrystalline elastic modulus (B, G and E) under pressure are calculated for the first time. Furthermore, the results suggest that the Sn2S3 is predicted to be mechanically stable in the range of pressure from 0 to 35 GPa in the light of the mechanical stability conditions. The Sn2S3 is found to be ductile from the value of B/G. With the increasing of pressure, the ductility of Sn2S3 enhances monotonously. The pressure effect on the energy band gap and density of states of Sn2S3 is also discussed, which indicates that the pressure makes the band gap of Sn2S3 decreased. The optical properties of Sn2S3 are calculated in the range 0–35 eV, and the results show that the Sn2S3 under pressure has stronger visible light absorption in comparison with 0 GPa.

scholarly journals First Principle Investigation of Electronic, Transport, and Bulk Properties of Zinc-Blende Magnesium Sulfide

Electronics ◽  
2020 ◽  
Vol 9 (11) ◽  
pp. 1791
Author(s):  
Uttam Bhandari ◽  
Blaise Awola Ayirizia ◽  
Yuriy Malozovsky ◽  
Lashounda Franklin ◽  
Diola Bagayoko
Keyword(s):  
Band Gap ◽  
Lattice Constant ◽  
Density Functional ◽  
Local Density ◽  
Computational Method ◽  
Physical Content ◽  
Conduction Bands ◽  
Zinc Blende ◽  
Densities Of States ◽  
Magnesium Sulfide

We have studied electronic, structural, and transport properties of zinc-blende magnesium sulfide (zb-MgS). We employed a local density approximation (LDA) potential and the linear combination of atomic orbitals (LCAO) method. Our computational method is able to reach the ground state of a material, as dictated by the second theorem of density functional theory (DFT). Consequently, our findings have the physical content of DFT and agree with available, corresponding experimental ones. The calculated band gap of zb-MgS, a direct gap equal to 4.43 eV, obtained at the experimental lattice constant of 5.620 Å, completely agrees with the experimental band gap of 4.45 ± 0.2 eV. We also report total (DOS) and partial (pDOS) densities of states, electron and hole effective masses, the equilibrium lattice constant, and the bulk modulus. The calculated pDOS also agree with the experiment for the description of the states at the top and the bottom of the valence and conduction bands, respectively.

scholarly journals Large Bandgap Topological Insulator in Oxide APoO3 (A = Be, Mg, Ca, Sr, Ba, and Ra) Perovskite: An Ab Initio Study

2021 ◽  
Vol 11 (3) ◽  
pp. 1143
Author(s):  
Chi-Hsuan Lee ◽  
Jen-Chuan Tung
Keyword(s):  
Elastic Constants ◽  
Density Functional ◽  
Electric Polarization ◽  
Surface Band ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Conduction Channel ◽  
Out Of Plane ◽  
Surface Conduction ◽  
Theory Framework

Under the density functional theory framework, we have calculated the electronic and elastic properties of APoO3 (A = Be, Mg, Ca, Sr, Ba, and Ra) cubic perovskites. We found that CaPoO3, SrPoO3, BaPoO3, and RaPoO3 are topological insulators (TIs) with very large bandgaps of 0.861, 0.871, 0.820, and 0.810 eV, respectively. The nontrivial band topology together with the Z2 topological number of APoO3 perovskite are investigated. We also theoretically determine the three independent elastic constants C11, C12, and C44 of the APoO3 perovskite. The bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and anisotropy factor are also calculated from the obtained elastic constants. We found that the Debye temperature for the APoO3 perovskite is around 330-370 K. In the bulk APoO3 perovskite, if the center Po atom is shifted 0.09Å away from the center, the induced electric polarization is quite large, being around 0.02 C/m2. In the surface band calculation, we found that both AO and PoO2 surfaces give rise to contributions to the conduction channel. If the Po atom moves both in-plane and out-of-plane, we show that both electric polarization and topologically protect surface conduction states exist in APoO3 perovskite, indicating that these oxide APoO3 perovskites are ferroelectric TIs and might be useful for spintronic applications.

Influence of defect pairs in Ga-based ordered defect compounds: a hybrid density functional study

2020 ◽  
Vol 98 (8) ◽  
pp. 770-777
Author(s):  
Sudhir Kumar ◽  
Suman Joshi ◽  
Durgesh Kumar Sharma ◽  
Sushil Auluck
Keyword(s):  
Band Gap ◽  
Energy Band ◽  
Density Functional ◽  
Functional Study ◽  
Energy Band Gap ◽  
Functional Theory ◽  
Lattice Constants ◽  
Donor Acceptor ◽  
The Stability ◽  
Hybrid Density Functional

In the present paper, density functional theory (DFT) based calculations have been performed to predict the stability, electronic, and optical properties of Ga-rich ordered defect compounds (ODCs). The calculated lattice constants, bulk modulus, their pressure derivatives, and optical constants show good agreement with available experimental data. The hybrid exchange correlations functional have been considered to calculate ground state total energy and energy band gap of the material. The calculated formation energy of ODCs comes smaller than pure CuGaSe2 (CGS). Our calculated optical absorption coefficients indicate that the energy band gap of ODCs can be tuned by changing the number of donor–acceptor defect pairs ([Formula: see text]). The band offset has been calculated to understand the reason of band gap alteration while the number of defect pair changes. Our results may be helpful for other experiments to further improve the performance of ODCs.

STRUCTURAL PARAMETERS AND OPTOELECTRONIC PROPERTIES OF Mg-IV-V2 (IV=Si, Ge, Sn AND V=P, As) COMPOUNDS

2018 ◽  
Vol 25 (05) ◽  
pp. 1850108 ◽  
Author(s):  
M. IBRAHIM ◽  
HAYAT ULLAH ◽  
SAEED ULLAH JAN ◽  
MANZAR ALI ◽  
M. GULBAHAR ASHIQ
Keyword(s):  
Optical Properties ◽  
Band Gap ◽  
Density Functional ◽  
Structural Parameters ◽  
Visible Region ◽  
Functional Theory ◽  
Lattice Constants ◽  
Direct Band Gap ◽  
Semiconductor Behavior ◽  
Direct Band

Semiconductors are the backbone of the optoelectronic industry. Direct band gap materials in the visible energy region are highly desirable for the efficient optoelectronic applications. In this work, we have probed the structural, electronic and optical properties of Mg-IV-V2 (IV[Formula: see text]Si, Ge, Sn and V[Formula: see text]P, As) compounds by FP-LAPW calculations, based on density functional theory. Their crystal structure is chalcopyrite with space group of I-42d. The lattice constants of MgSiP2, MgSiAs2 and MgGeAs2 are consistent with experimental results. These compounds show semiconductor behavior with direct band gap ranging from 1.3–2.15[Formula: see text]eV. Optical properties were also investigated. Optical properties include real and imaginary parts of dielectric constant, energy loss function, refraction and reflection. Direct band gap nature and good response in the visible region of these compounds predict their usefulness in optoelectronic devices.

scholarly journals Electronic properties of palladium diselenide by density functional theory

2017 ◽  
Vol 13 (3) ◽  
Author(s):  
Ying Xuan Ng ◽  
Rashid Ahmed ◽  
Abdullahi Lawal ◽  
Bakhtiar Ul Haq ◽  
Afiq Radzwan ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Band Gap ◽  
Electronic Properties ◽  
Density Functional ◽  
Band Gap Energy ◽  
Partial Density ◽  
Full Potential ◽  
Functional Theory ◽  
Lattice Constants ◽  
Gap Energy

The knowledge of the structural and electronic properties of a material is important in various applications such as optoelectronics and thermoelectric devices. In this study, we are using full potential linearized augmented plane wave method framed within density functional theory provided by WIEN2k to optimize the structure of PdSe2 in orthorhombic (Pbca) phase and calculate its electronic properties. With the implementation of local density approximation (LDA), Perdew-Burke-Ernzerhof parameterization of generalized gradient approximation (PBE-GGA), Wu-Cohen parameterization of GGA (WC-GGA), and PBE correction for solid GGA (PBEsol-GGA), the computed results of lattice constants are found to be within 5% error with the experiment data. Also, our calculated indirect band gap energy was found to be ~0.24 eV by LDA along with modified Becke-Johnson potential functional (mBJ) with experimental lattice constants and ~0.52 eV by using PBE-GGA with optimized lattice constants. However, the effect of spin-orbit coupling is not found too much on the band gap energy. By analyzing the partial density of states, we identify that d-orbital of Pd is demonstrating a slightly more significant contribution to both the valence and conduction band near to Fermi level which is also in agreement with the previous first principles study.

Efficient Prediction of Structural and Electronic Properties of Hybrid 2D Materials Using DFT and Machine Learning

2018 ◽  
Author(s):  
Sherif Tawfik ◽  
Olexandr Isayev ◽  
Catherine Stampfl ◽  
Joseph Shapter ◽  
David Winkler ◽  
...  
Keyword(s):  
Machine Learning ◽  
Band Gap ◽  
Density Functional ◽  
2D Materials ◽  
Van Der Waals ◽  
Building Blocks ◽  
Machine Learning Techniques ◽  
Interlayer Distance ◽  
Computational Screening ◽  
Wide Range

Materials constructed from different van der Waals two-dimensional (2D) heterostructures offer a wide range of benefits, but these systems have been little studied because of their experimental and computational complextiy, and because of the very large number of possible combinations of 2D building blocks. The simulation of the interface between two different 2D materials is computationally challenging due to the lattice mismatch problem, which sometimes necessitates the creation of very large simulation cells for performing density-functional theory (DFT) calculations. Here we use a combination of DFT, linear regression and machine learning techniques in order to rapidly determine the interlayer distance between two different 2D heterostructures that are stacked in a bilayer heterostructure, as well as the band gap of the bilayer. Our work provides an excellent proof of concept by quickly and accurately predicting a structural property (the interlayer distance) and an electronic property (the band gap) for a large number of hybrid 2D materials. This work paves the way for rapid computational screening of the vast parameter space of van der Waals heterostructures to identify new hybrid materials with useful and interesting properties.

scholarly journals Enhanced surface state protection and band gap in the topological insulator PbBi4Te4S3

2018 ◽  
Vol 2 (10) ◽  
Author(s):  
K. Sumida ◽  
T. Natsumeda ◽  
K. Miyamoto ◽  
I. V. Silkin ◽  
K. Kuroda ◽  
...  
Keyword(s):  
Band Gap ◽  
Topological Insulator ◽  
Surface State ◽  
Enhanced Surface ◽  
State Protection
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