Optical band gap of SrTcO3 from first-principles calculations

2014 ◽  
Vol 28 (06) ◽  
pp. 1450049 ◽  
Author(s):  
Cheng-Min Dai ◽  
Chun-Lan Ma
Keyword(s):  
Band Structure ◽  
Band Gap ◽  
Magnetic Moment ◽  
Optical Band Gap ◽  
Tight Binding ◽  
Local Magnetic Moment ◽  
Exchange Constant ◽  
Generalized Gradient ◽  
Direct Band ◽  
State Band

Although there are intensive studies on technetium oxide SrTcO 3 recently, its ground-state band structure has never been given and no consensus on its band gap is obtained. We use the generalized gradient approximation (GGA) with on-site Coulomb corrections (GGA + U) method to study its band structure and the optical band gap. A series of on-site interaction U and J values are employed in the calculations and the concomitant evolutions of the electronic structure, local magnetic moment of technetium ( Tc ), the exchange constant and the Néel temperature are investigated. The inter-site exchange constant between antiferromagnetic Tc atoms through medium oxygen is found to increase firstly and then decrease with an increasing U, in agreement with the trend obtained by tight-binding method. The appropriate on-site U and J values are calibrated by comparing the calculated local magnetic moment of Tc with the experimental value. It is found that when U = 2.3 eV, J = 0.3 eV are included for Tc 4d in GGA + U calculations, the local magnetic moment of Tc in orthorhombic SrTcO 3 is 2.01 μB, the same as the experimental value obtained at 4 K. The calculated band structure shows that the band gap is a direct band gap with a magnitude of 1.61 eV.

scholarly journals Computational Investigation of the Folded and Unfolded Band Structure and Structural and Optical Properties of CsPb(I1−xBrx)3 Perovskites

Crystals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 342 ◽  
Author(s):  
Hamid M. Ghaithan ◽  
Zeyad A. Alahmed ◽  
Andreas Lyras ◽  
Saif M. H. Qaid ◽  
Abdullah S. Aldwayyan
Keyword(s):  
Optical Properties ◽  
Band Structure ◽  
Band Gap ◽  
Spectral Weight ◽  
Band Gap Energy ◽  
Full Potential ◽  
Generalized Gradient ◽  
Electronic And Optical Properties ◽  
Generalized Gradient Approximation ◽  
Direct Band

The structural, electronic, and optical properties of inorganic CsPb(I1−xBrx)3 compounds were investigated using the full-potential linear augmented-plane wave (FP-LAPW) scheme with a generalized gradient approximation (GGA). Perdew–Burke–Ernzerhof generalized gradient approximation (PBE-GGA) and modified Becke–Johnson GGA (mBJ-GGA) potentials were used to study the electronic and optical properties. The band gaps calculated using the mBJ-GGA method gave the best agreement with experimentally reported values. CsPb(I1−xBrx)3 compounds were wide and direct band gap semiconductors, with a band gap located at the M point. The spectral weight (SW) approach was used to unfold the band structure. By substituting iodide with bromide, an increase in the band gap energy (Eg) values of 0.30 and 0.55 eV, using PBE-GGA and mBJ-GGA potentials, respectively, was observed, whereas the optical property parameters, which were also investigated, demonstrated the reverse effect. The high absorption spectra in the ultraviolet−visible energy range demonstrated that CsPb(I1−xBrx)3 perovskite could be used in optical and optoelectronic devices by partly replacing iodide with bromide.

scholarly journals Carbon-Based Band Gap Engineering in the h-BN Analytical Modeling

Materials ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1026
Author(s):  
Mohammad Taghi Ahmadi ◽  
Ahmad Razmdideh ◽  
Seyed Saeid Rahimian Koloor ◽  
Michal Petrů
Keyword(s):  
Boron Nitride ◽  
Band Gap ◽  
Density Functional ◽  
Hexagonal Boron Nitride ◽  
Tight Binding ◽  
Band Gap Energy ◽  
Specific Structure ◽  
Partial Substitution ◽  
Generalized Gradient ◽  
Complete Replacement

The absence of a band gap in graphene is a hindrance to its application in electronic devices. Alternately, the complete replacement of carbon atoms with B and N atoms in graphene structures led to the formation of hexagonal boron nitride (h-BN) and caused the opening of its gap. Now, an exciting possibility is a partial substitution of C atoms with B and N atoms in the graphene structure, which caused the formation of a boron nitride composite with specified stoichiometry. BC2N nanotubes are more stable than other triple compounds due to the existence of a maximum number of B–N and C–C bonds. This paper focused on the nearest neighbor’s tight-binding method to explore the dispersion relation of BC2N, which has no chemical bond between its carbon atoms. More specifically, the band dispersion of this specific structure and the effects of energy hopping in boron–carbon and nitrogen–carbon atoms on the band gap are studied. Besides, the band structure is achieved from density functional theory (DFT) using the generalized gradient approximations (GGA) approximation method. This calculation shows that this specific structure is semimetal, and the band gap energy is 0.167 ev.

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.

First-principles study on the band structure, magnetic and elastic properties of half-metallic Cr2MnAl

2015 ◽  
Vol 29 (24) ◽  
pp. 1550139 ◽  
Author(s):  
Santao Qi ◽  
Chuan-Hui Zhang ◽  
Bao Chen ◽  
Jiang Shen
Keyword(s):  
Band Structure ◽  
Band Gap ◽  
Elastic Properties ◽  
Density Functional ◽  
Stable State ◽  
Generalized Gradient ◽  
Half Metallic ◽  
Text Type ◽  
Calculation Results ◽  
Indirect Band Gap

In this study, we have investigated the structural, electronic, magnetic and elastic properties of the full-Heusler [Formula: see text] alloy in the framework of density functional theory with generalized gradient approximation (GGA). The calculated results showed that [Formula: see text] was stable in ferrimagnetic configuration and crystallized in the [Formula: see text]-type structure. From the band structure and density of states calculation results, we concluded that [Formula: see text] belongs to a kind of half-metallic compound with an indirect band gap of 0.37 eV. Immediately thereafter, we have analyzed the origin of half-metallic band gap. The total magnetic moment of [Formula: see text] at the stable state is [Formula: see text] per formula unit, obeying the Slater–Pauling rule [Formula: see text]. In addition, various mechanical properties have been obtained and discussed based on the three principle elastic tensor elements [Formula: see text] and [Formula: see text] for the first time in the present work. We expect that our calculated results may trigger the application of [Formula: see text] in future spintronics field.

Structural and Magnetic Study on the Effect of Substitution of Cobalt by d-Valent Elements of Co2FeSi Heusler Alloy

2016 ◽  
Vol 708 ◽  
pp. 37-41
Author(s):  
Muhammad Noor Syazwan Saimin ◽  
Siti Sumaiyah Sheikh Abdul Aziz ◽  
A.M.M. Ali ◽  
Oskar Hasdinor Hassan ◽  
Muhd Zu Azhan Yahya ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Electronic Structure ◽  
Band Structure ◽  
Fermi Level ◽  
Density Of States ◽  
Magnetic Moment ◽  
Local Magnetic Moment ◽  
Half Metallic ◽  
New States ◽  
Full Heusler

In this paper, the effect of substitution of Co by d-valent elements such as Ag and Pt on electronic structure and magnetic properties of full Heusler type Co2FeSi alloys was investigated. Structural study reveals the presence of a small gap in the minority band structure around the vicinity of the Fermi level on Co2FeSi resulting to half-metallic behaviour. However, CoFeSiAg and CoFeSiPt cannot preserved the half-metalicity due to disappearing of the gap in the minority band structure due to the creation of new states around the Fermi level in the minority density of states. The variation in the magnetic moment of Co2FeSi with change of the atoms was attributed to the change in the local magnetic moment of atoms.

Atomic and Electronic Structure of LaAlO3 and LaAlO3:Mg from First-Principles Calculations

2009 ◽  
Vol 79-82 ◽  
pp. 1257-1260
Author(s):  
Li Guan ◽  
Li Tao Jin ◽  
Wei Zhang ◽  
Qiang Li ◽  
Jian Xin Guo ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Band Structure ◽  
Band Gap ◽  
Density Functional ◽  
Lattice Structure ◽  
Cell Structure ◽  
Functional Theory ◽  
Super Cell ◽  
Direct Band ◽  
Experimental Values

In the present paper, the lattice structure, band structure and density of state of LaAlO3 and LaAlO3:Mg are calculated by first-principle method based on density functional theory. Firstly, we select the different cutoff energy and k-point grid in the calculations, and obtain the most stable geometry structure of single crystal LaAlO3. The calculated lattice parameters are a=b=5.441 Å, c=13.266 Å, which matches with experimental values. To deeply understand the electronic structure of LaAlO3, a 2×1×1 super-cell structure is established and the doping concentration of Mg at Al sites is 25%. From the band structure and density of states, it can be seen that LaAlO3 has a direct band gap Eg=3.6 eV. However, LaAlO3:Mg has a larger band gap Eg=3.89 eV and the Fermi level enters into the valence band, which indicates the holes are introduced. The calculated results show that the conductivity of LaAlO3:Mg is better than pure LaAlO3, which is in good agreement with experimental results.

scholarly journals Tight–Binding Analysis of Electronic Structure of Germanene Sheet and Nanoribbons Including Stone-Wales Defect

2021 ◽  
Author(s):  
Komeil Rahmani ◽  
Saeed Mohammadi
Keyword(s):  
Band Structure ◽  
Band Gap ◽  
Energy Band ◽  
Dirac Point ◽  
Tight Binding ◽  
Topological Defects ◽  
Energy Band Structure ◽  
Fermi Velocity ◽  
Tight Binding Approximation ◽  
Wales Defect

Abstract In this paper, we investigate the electronic characteristics of germanene using the tight binding approximation. Germanene as the germanium-based analogue of graphene has attracted much research interest in recent years. Our analysis is focused on the pristine sheet of germanene as well as defective monolayer. The Stone-Wales defect, which is one of the most common topological defects in such structures, is considered in this work. Not only the infinite sheet of germanene but also the germanene nanoribbons in different orientations are analyzed. The obtained results show that applying the Stone–Wales defect into the germanene monolayer changes the energy band structure; the E-k curves around the Dirac point are no longer linear, a band gap is opened, and the Fermi velocity is reduced to half of that of defect-free germanene. In the case of nanoribbon structures, the armchair germanene nanoribbons with nanoribbon widths of 3p and 3p+1 reveal the semiconductor behaviour. However, armchair germanene nanoribbon with width of 3p+2 is semi-metal. After applying the Stone–Wales defect, the band gap of armchair germanene nanoribbons with widths of 3p and 3p+1 is reduced and it is increased for the width of 3p+2. Furthermore, there is no band gap in the energy band structure of zigzag germanene nanoribbon and the metallic behaviour is obvious.

scholarly journals Temperature dependent Band gap Correction model using tight-binding approach for UTB device simulations

2022 ◽  
Author(s):  
Nalin Vilochan Mishra ◽  
Ravi Solanki ◽  
Harshit Kansal ◽  
Aditya S Medury
Keyword(s):  
Band Structure ◽  
Band Gap ◽  
Tight Binding ◽  
Thin Body ◽  
Temperature Dependent ◽  
Minor Variation ◽  
Correction Model ◽  
Wide Range ◽  
Channel Thickness ◽  
Semi Empirical

<div>Ultra-thin body (UTB) devices are being used in many electronic applications operating over a wide range of temperatures. The electrostatics of these devices depends on the band structure of the channel material, which varies with temperature as well as channel thickness. The semi-empirical tight binding (TB) approach is widely used for calculating channel thickness dependent band structure of any material, at a particular temperature, where TB parameters are defined. For elementary semiconductors like Si, Ge and compound semiconductors like GaAs, these TB parameters are generally defined at only 0 K and 300 K. This limits the ability of the TB approach to simulate the electrostatics of these devices at any other intermediate temperatures.</div><div>In this work, we analyze the variation of band structure for Si, Ge and GaAs over different channel thicknesses at 0 K and 300 K (for which TB parameters are available), and show that the band curvature at the band minima has minor variation with temperature, whereas the change of band gap significantly affects the channel electrostatics. Based on this finding, we propose an approach to simulate the electrostatics of UTB devices, at any temperature between 0 K and 300 K, using TB parameters defined at 0 K, along with a suitable channel thickness and temperature dependent band gap correction. </div>

Sign in / Sign up

Export Citation Format

Share Document