scholarly journals ATiO3 (A = Ca, Sr, Ba & BP) Pervoskites in Cubic and Tetragonal Phase using TB-LMTO-ASA Method

2019 ◽  
Vol 9 (2S2) ◽  
pp. 707-714
Keyword(s):  
Band Gap ◽  
Density Of States ◽  
Tetragonal Phase ◽  
Density Functional ◽  
Tight Binding ◽  
Partial Density ◽  
Cubic Phase ◽  
Lmto Method ◽  
Orbital Position ◽  
Sphere Approximation

Ground state properties of ATiO3 (A = Ca, Sr, Ba & Pb) pervoskite structures in cubic and tetragonal phase were studied by tight binding linear muffin-tin orbital (TB-LMTO) method in the framework of density functional theory (DFT) with the atomic-sphere approximation (ASA). The total energy of all the compounds come under the above said structures have shown that the cubic phase is the stable structure in the ambient condition. Among these pervoskites maximum bulk modulus was obtained for BaTiO3 . Direct (cubic) and indirect (tetragonal) band gap was observed from the band structure calculations and the values fall within the range of 1.5 – 1.7 eV. Electron distribution of each element in the valence and conduction bands was clearly obtained from the density of states (DOS) and partial density of states (PDOS) for all the compounds. The magnetization values were found in the range of 0.4 – 0.56 x 10-5µB. The‘d’ orbital position of Ti was observed for all the ABO3 compounds and shifted away from the Fermi level except for Ti in BaTiO3 . The refractive indices of the pervoskites were calculated from the energy band gap and the value is above 3 for all the compounds.

Electronic Properties of Calcium and Zirconium Co-Doped BaTiO3

2020 ◽  
Vol 1010 ◽  
pp. 308-313
Author(s):  
Akeem Adekunle Adewale ◽  
Abdullah Chik ◽  
Ruhiyuddin Mohd Zaki
Keyword(s):  
Band Gap ◽  
Electronic Properties ◽  
Density Of States ◽  
Energy Band ◽  
Density Functional ◽  
Partial Density ◽  
Total Density ◽  
Energy Band Gap ◽  
Wide Energy ◽  
Direct Band

Barium titanate (BaTiO3) is a perovskite based oxides with many potential application in electronic devices. From experimental report BaTiO3 has wide energy band gap of about 3.4 eV which by doped with Ca and Zr at A- and B- sites respectively can enhance their piezoelectric properties. Using first principles method within the density functional theory (DFT) as implement in Quantum Espresso (QE) with the plane wave pseudo potential function, the influence of the Ca and Zr doping in BaTiO3 are studied via electronic properties: band structure, total density of states (TDOS) and partial density of states (PDOS). The energy band gap calculated was underestimation which is similar to other DFT work. Two direct band gap where observed in Ba0.875Ca0.125Ti0.875Zr0.125O3 sample at Γ- Γ (2.31 eV) and X- X (2.35 eV) symmetry point.

scholarly journals Study on Electronic and Optical Properties of Graphene Oxide Under an External Electric Field From First-principles

2021 ◽  
Author(s):  
Abdehafid Najim ◽  
Omar BAJJOU ◽  
Mustapha BOULGHALLAT ◽  
Mohammed Khenfouch ◽  
Khalid Rahmani
Keyword(s):  
Optical Properties ◽  
Graphene Oxide ◽  
Electric Field ◽  
Band Gap ◽  
External Electric Field ◽  
Density Of States ◽  
Density Functional ◽  
Partial Density ◽  
Total Density ◽  
Electronic And Optical Properties

Abstract Electronic and optical properties of graphene oxide (GO), under an external electric field (Eext) applied in three directions of space (x, y, z), are investigated using the density functional theory (DFT). The application of the Eext, causes a significant modifications to the electronic and optical properties of GO material. It has change the band gap, total density of states (TDOS), partial density of states (PDOS), absorption coefficient (α), dielectric function, optical conductivity, refractive index and loss function. The band gap of GO layer increases under the effects of the Eext, applied in x and y directions. On the other hand, for z direction, the band gap decreases by the effects of the Eext. The peaks of the TDOS around the Fermi level, change by the Eext applied in (x, y, z) directions. The α peaks of the GO sheet, decreases by the Eext applied in x direction, and increases if Eext applied in y and z directions. It is found that, the electronic and optical properties of GO layer, could be affected by the effects of the Eext and by its direction of application.

scholarly journals DFT Study on Structural, Electronic and Optical Properties of Ag-Doped SrTiO3 Perovskite for Optoelectronic Applications

2021 ◽  
Author(s):  
Jalil Rehman ◽  
M.Awais Rehman ◽  
Muhammad Bilal Tahir ◽  
Muhammad Usman ◽  
Faisal Iqbal
Keyword(s):  
Optical Properties ◽  
Band Gap ◽  
Density Of States ◽  
Density Functional ◽  
Partial Density ◽  
Electronic Band ◽  
Ag Doping ◽  
Direct Band Gap ◽  
Direct Band ◽  
Optoelectronic Applications

This study addresses the first-principles analysis using generalized gradient approximation (GGA), which is pillared on density functional theory (DFT), to find the effects of silver (Ag) doping on SrTiO3 structurally, electronically and optical properties. As Ag doping into SrTiO3, we see a small decrease in the volume of unit cell. Moreover, Ag-doping adds new states in SrTiO3 at Brillouin zone symmetry points, transferring host material’s indirect band gap to a direct band gap. Ag doping in SrTiO3 results in the transfer density of states to smaller energies and increase in interaction among Ag atom and its surrounding atoms. Moreover, at the conduction band, the partial density of states (PDOS) of SrTiO3 changes generally. As a result, we conclude that Ag doping has an effect on the electronic band structure of SrTiO3. SrTiO3 doping with Ag has improved optical properties and its ability of converting to direct band gap results it in a perfect choice for optoelectronic applications.

scholarly journals Ultra-wide bandgap semiconductor behavior of NaCaF3 fluoro-perovskite with external static isotropic pressure and its impact on optical properties: First-principles computation

2021 ◽  
Author(s):  
Syed Sajid Ali Gillani ◽  
Nisar Fatima ◽  
M. Shakil ◽  
R. Kiran ◽  
M. B. Tahir ◽  
...  
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Band Gap ◽  
Density Of States ◽  
Density Functional ◽  
External Pressure ◽  
Partial Density ◽  
Total Density ◽  
Isotropic Pressure ◽  
The Impact

Abstract A comprehensive theoretical study to investigate the outcomes of externally applied static isotropic pressure (0 GPa - 50 GPa) on electronic, optical and structural properties of NaCaF3, using density functional theory (DFT) based CASTEP (Cambridge Serial Total Energy Package) code with ultra-soft pseudo-potential USP plane wave and Perdew Burke Ernzerhof (PBE) exchange-correlation functional of Generalized Gradient Approximation (GGA), is reported. The electronic bandgap shows the increasing trend 4.773 eV - 6.203 eV (direct bandgap) with increasing external pressure. The increase in bandgap is significant up to 20 GPa as compared to higher external pressures. The mystery of increasing band gap is nicely decoded by total density of states (TDOS) and elemental partial density of states (EPDOS). Optical properties have been calculated to analyze the impact of increment in band gap on them. We observed that highest peak of energy loss function L(w) shows the blue shift which confirms the increment of band gap. At zero photon energy, for 0 GPa, the static refractive index n(w) has value of 1.4456. After applying external pressure, there is a slight increase in n(w) which favors the semiconducting behavior of ternary compound. The energy points at which the absorption peak is maxima, the refractive index has lowest value.

scholarly journals First-principles study of C cites vacancy defects in water adsorbed Graphene

2020 ◽  
pp. 19-29
Author(s):  
Hari Krishna Neupane ◽  
Narayan Prasad Adhikari
Keyword(s):  
Magnetic Properties ◽  
Band Gap ◽  
Density Of States ◽  
Magnetic Moment ◽  
First Principles ◽  
Density Functional ◽  
Partial Density ◽  
Dangling Bonds ◽  
Graphene Surface ◽  
Vacancy Defects

 The electronic and magnetic properties of water adsorbed graphene (wad – G), single carbon (1C) atom vacancy defects in water adsorbed graphene (1Catom-vacancy – wad – G) and double carbon (2C) atoms vacancy defects in water adsorbed graphene (2Catom-vacancy – wad – G) materials are studied by first-principles calculations within the frame work of density functional theory (DFT) using computational tool Quantum ESPRESSO (QE) code. We have calculated the binding energy of wad – G, 1Catom-vacancy – wad – G and 2Catom-vacancy – wad – G materials, and then found that non-defects geometry is more compact than vacancy defects geometries. From band structure calculations, we found that wad – G is zero band gap semiconductor, but 1Catom-vacancy – wad – G and, 2Catom-vacancy – wad – G materials have metallic properties. Hence, zero band gap semiconductor changes to metallic nature due to C sites vacancy defects in its structures. We have investigated the magnetic properties of wad – G and its C sites vacancy defects materials by using Density of States (DOS) and Partial Density of States (PDOS) calculations. We found that wad – G is non- magnetic material. 1C atom vacancy defects in graphene surface of wad – G is induced magnetization by the re-bonding of two dangling bonds and acquiring significant magnetic moment (0.11 µB/ cell) through remaining unsaturated dangling bond. But, 2C atoms vacancy defects in graphene surface of wad – G induced low value of magnetic moment (+0.03 µB/ cell) than 1C atom vacancy defects in structure, which is due to no dangling bonds present in the structure. Therefore, non-magnetic, wad – G changes to magnetic, 1Catom-vacancy – wad – G and, 2Catom-vacancy – wad – G materials due to C sites vacancy defects in wad – G structure. The 2p orbital of carbon atoms has main contribution of magnetic moment in defects structures.

scholarly journals Hydration Dependent Band Gap Tunability of Self-Assembled Phenylalanine-Tryptophan Nanotubes

2020 ◽  
Author(s):  
Hugo Souza ◽  
Antonio Chaves Neto ◽  
Francisco Sousa ◽  
Rodrigo Amorim ◽  
Alexandre Reily Rocha ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Band Gap ◽  
Electronic Properties ◽  
Building Block ◽  
Density Functional ◽  
Tight Binding ◽  
Water Molecules ◽  
Confined Water ◽  
Functional Theory ◽  
Tight Binding Method

In this work, we investigate the effects of building block separation of Phenylalanine-Tryptophan nanotube induced by the confined water molecules on the electronic properties using density-functional theory based tight-binding method. <div><br></div>

scholarly journals Organically interconnected graphene flakes: A flexible 3-D material with tunable electronic bandgap

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
E. Klontzas ◽  
E. Tylianakis ◽  
V. Varshney ◽  
A. K. Roy ◽  
G. E. Froudakis
Keyword(s):  
Chemical Composition ◽  
Band Gap ◽  
Electronic Properties ◽  
Flexible Electronics ◽  
Density Functional ◽  
Organic Molecule ◽  
Tight Binding ◽  
Structural And Electronic Properties ◽  
Graphene Flakes ◽  
Band Gap Tuning

Abstract The structural and electronic properties of molecularly pillared graphene sheets were explored by performing Density Functional based Tight Binding calculations. Several different architectures were generated by varying the density of the pillars, the chemical composition of the organic molecule acting as a pillar and the pillar distribution. Our results show that by changing the pillars density and distribution we can tune the band gap transforming graphene from metallic to semiconducting in a continuous way. In addition, the chemical composition of the pillars affects the band gap in a lesser extent by introducing additional states in the valence or the conduction band and can act as a fine band gap tuning. These unique electronic properties controlled by design, makes Mollecular Pillared Graphene an excellent material for flexible electronics.

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.

First-principles investigation of the structural, elastic, electronic, and optical properties of semiconducting AgBr1–xIx (0 ≤ x ≤ 1) ternary alloys in rock-salt and zinc blende structures

2020 ◽  
Vol 98 (9) ◽  
pp. 834-848
Author(s):  
H. Rekab-Djabri ◽  
Mohamed Drief ◽  
Manal M. Abdus Salam ◽  
Salah Daoud ◽  
F. El Haj Hassan ◽  
...  
Keyword(s):  
Optical Properties ◽  
Band Gap ◽  
Rock Salt ◽  
Density Functional ◽  
Local Density ◽  
Ternary Alloys ◽  
Full Potential ◽  
Zinc Blende ◽  
Lmto Method ◽  
Direct Band

In this work, first principle calculations of the structural, electronic, elastic, and optical properties of novel AgBr1–xIx ternary alloys in rock-salt (B1) and zinc-blende (B3) structures are presented. The calculations were performed using the full-potential linear muffin-tin orbital (FP-LMTO) method within the framework of the density functional theory (DFT). The exchange and correlation potentials were treated according to the local density approximation (LDA). The lattice constants for the B1 and B3 phases versus iodide concentration (x) were found to deviate slightly from the linear relationship of Vegard’s law. The calculated electronic properties showed that AgBr1–xIx alloys in the B3 structure have a direct band gap (Γ – Γ) for all concentrations of x, which means that they can be used in long-wavelength optoelectronic applications, while in the B1 structure they have an indirect (Γ – R) band gap. The elastic constants Cij, shear modulus G, Young’s modulus E, Poisson’s ratio ν, index of ductility B/G, sound velocities vt, vl, and vm, and Debye temperature θD were also reported and analyzed. By incorporating the basic optical properties, we discussed the dielectric function, refractive index, optical reflectivity, absorption coefficient, and optical conductivity in terms of incident photon energy up to 13.5 eV. The present results were found to be in good agreement with the available experimental and other theoretical results.

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.

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