scholarly journals Electron Polarons in Lithium Niobate: Charge Localization, Lattice Deformation, and Optical Response

Crystals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 542
Author(s):  
Falko Schmidt ◽  
Agnieszka L. Kozub ◽  
Uwe Gerstmann ◽  
Wolf Gero Schmidt ◽  
Arno Schindlmayr
Keyword(s):  
Lithium Niobate ◽  
Optical Absorption ◽  
Band Gap ◽  
Density Of States ◽  
Density Functional ◽  
Conduction Band Edge ◽  
Defect Level ◽  
Gw Approximation ◽  
Charge Localization ◽  
Excitonic Effects

Lithium niobate (LiNbO3), a material frequently used in optical applications, hosts different kinds of polarons that significantly affect many of its physical properties. In this study, a variety of electron polarons, namely free, bound, and bipolarons, are analyzed using first-principles calculations. We perform a full structural optimization based on density-functional theory for selected intrinsic defects with special attention to the role of symmetry-breaking distortions that lower the total energy. The cations hosting the various polarons relax to a different degree, with a larger relaxation corresponding to a larger gap between the defect level and the conduction-band edge. The projected density of states reveals that the polaron states are formerly empty Nb 4d states lowered into the band gap. Optical absorption spectra are derived within the independent-particle approximation, corrected by the GW approximation that yields a wider band gap and by including excitonic effects within the Bethe–Salpeter equation. Comparing the calculated spectra with the density of states, we find that the defect peak observed in the optical absorption stems from transitions between the defect level and a continuum of empty Nb 4d states. Signatures of polarons are further analyzed in the reflectivity and other experimentally measurable optical coefficients.

Structural and Electronic Properties of Oxygen Vacancies in Monoclinic HfO2

2007 ◽  
Vol 996 ◽  
Author(s):  
Peter Broqvist ◽  
Alfredo Pasquarello
Keyword(s):  
Oxygen Vacancy ◽  
Optical Absorption ◽  
Total Energy ◽  
Band Gap ◽  
Electronic Properties ◽  
Density Functional ◽  
Oxygen Vacancies ◽  
Structural And Electronic Properties ◽  
Defect Levels ◽  
Hybrid Density Functional

AbstractWe study structural and electronic properties of the oxygen vacancy in monoclinic HfO2 for five different charge states. We use a hybrid density functional to accurately reproduce the experimental band gap. To compare with measured defect levels, we determine total-energy differences appropriate to the considered experiments. Our results show that the oxygen vacancy can consistently account for the defect levels observed in optical absorption, direct electron injection, and trap-assisted conduction experiments.

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.

Properties of Silicon Carbide Polytypes under High Pressure Influence Calculated Using DFT

2017 ◽  
Vol 268 ◽  
pp. 138-142 ◽  
Author(s):  
Alham Mohamed M. Emhemed ◽  
Noriza Ahmad Zabidi ◽  
Ahmad Nazrul Rosli
Keyword(s):  
Silicon Carbide ◽  
Band Gap ◽  
Density Functional ◽  
Hexagonal Structure ◽  
Lattice Parameters ◽  
Conduction Band Edge ◽  
Dynamic Simulations ◽  
Functional Theory ◽  
Structural And Electronic Properties ◽  
Gap Width

Theoretical molecular dynamic simulations based on plane-wave and pseudopotential density functional theory (DFT) calculations with CASTEP code were employed to explore the pressure influence on the properties of silicon carbide polytypes. The changes in lattice and electronic structures of 2H-, 4H-, and 6H-SiC polytypes at room temperature were investigated when pressures from 10 GPa to 200 GPa were applied. It’s found that the applied pressures didn’t cause a change in the hexagonal structure of the crystals, however the structural and electronic properties clearly affected by the compression. The dependences of volume reduction (V/Vo) and lattice parameters (a and c) on pressure were obtained successfully. The lattice parameters of the polytypes and c/a ratio showed a same trend under the compression with a clear similarity between 4H and 6H. The total energy-volume and enthalpy-pressure relations were estimated. The calculated energy gaps showed a reduction in the band gap width of 4H and 6H with the pressure increase while 2H band gap increased gradually with pressure. The tendency toward decreasing the density of state (DOS) at the conduction band edge was similar among the polytypes.

scholarly journals Band gap reduction in InNxSb1-x alloys: Optical absorption, k · P modeling, and density functional theory

2016 ◽  
Vol 109 (13) ◽  
pp. 132104 ◽  
Author(s):  
W. M. Linhart ◽  
M. K. Rajpalke ◽  
J. Buckeridge ◽  
P. A. E. Murgatroyd ◽  
J. J. Bomphrey ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Optical Absorption ◽  
Band Gap ◽  
Density Functional ◽  
Functional Theory

scholarly journals Phase transition-induced band edge engineering of BiVO4 to split pure water under visible light

2015 ◽  
Vol 112 (45) ◽  
pp. 13774-13778 ◽  
Author(s):  
Won Jun Jo ◽  
Hyun Joon Kang ◽  
Ki-Jeong Kong ◽  
Yun Seog Lee ◽  
Hunmin Park ◽  
...  
Keyword(s):  
Phase Transition ◽  
Visible Light ◽  
Band Gap ◽  
Conduction Band ◽  
Density Functional ◽  
Density Functional Theory Calculation ◽  
Pure Water ◽  
Volume Growth ◽  
Band Edge ◽  
Conduction Band Edge

Through phase transition-induced band edge engineering by dual doping with In and Mo, a new greenish BiVO4 (Bi1-XInXV1-XMoXO4) is developed that has a larger band gap energy than the usual yellow scheelite monoclinic BiVO4 as well as a higher (more negative) conduction band than H+/H2 potential [0 VRHE (reversible hydrogen electrode) at pH 7]. Hence, it can extract H2 from pure water by visible light-driven overall water splitting without using any sacrificial reagents. The density functional theory calculation indicates that In3+/Mo6+ dual doping triggers partial phase transformation from pure monoclinic BiVO4 to a mixture of monoclinic BiVO4 and tetragonal BiVO4, which sequentially leads to unit cell volume growth, compressive lattice strain increase, conduction band edge uplift, and band gap widening.

THEORETICAL STUDY OF THE BAND GAP OF SrSe AND SrTe IN GW APPROXIMATION

2011 ◽  
Vol 25 (23) ◽  
pp. 1905-1914
Author(s):  
XIAO LING ZHU ◽  
HONG ZHANG ◽  
XIN LU CHENG
Keyword(s):  
Band Gap ◽  
Density Functional ◽  
Theoretical Study ◽  
Generalized Gradient ◽  
Gw Approximation ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Structural And Electronic Properties ◽  
Experimental Values ◽  
Interaction Approximation

Using the first-principles pseudopotential method within a generalized gradient approximation of the density functional theory, the structural and electronic properties of SrSe and SrTe have been studied. The calculated lattice parameters are in excellent agreement with experimental values, whereas the error in the minimum gap value is as high as 43.25% in SrSe . To get reliable band gap values of SrSe and SrTe , we employ the GW (G is the Green's function and W is the screened Coulomb interaction) approximation method. The result in GW approximation improves the band gap value of the SrSe greatly and agrees with the value of experimental measurement.

Optoelectronic Analysis of CdGa2X4 (X= S, Se): A Promising Material for Solar Cells

2017 ◽  
Vol 900 ◽  
pp. 69-73 ◽  
Author(s):  
Pancham Kumar ◽  
Jagrati Sahariya ◽  
Amit Soni ◽  
K.C. Bhamu
Keyword(s):  
Solar Cell ◽  
Band Gap ◽  
Density Of States ◽  
Density Functional ◽  
Visible Spectrum ◽  
Full Potential ◽  
Functional Theory ◽  
Augmented Plane Wave ◽  
Direct Band Gap ◽  
Direct Band

In this paper, the optoelectronic nature of the CdGa2X4 (X = S, Se) solar cell materials are examined using full potential linear augmented plane wave (FP-LAPW) method as embodied in WIEN2K code. In present computation, we have used most suitable modified Backe-Johnson (mBJ) potential under the framework of density functional theory (DFT). The calculated electronic properties like energy band structure and density of states spectra show that these materials exhibit a direct band gap (Γ–Γ) result of 3.22 eV and 2.36 eV for CdGa2S4 and CdGa2Se4 compounds, respectively. Absorption spectra for CdGa2X4 (X = S, Se) compounds have been studied and it has been found that above the band gap, absorption are taking place and it covers wide visible spectrum energy range. On the basis of calculated band gap, density of states and absorption coefficient spectra, it is found that these compounds can be suitably applicable in optoelectronic devices such as solar cell. The evaluated properties pose well agreement with available experimental data.

Electronic excitations of stable fullerene-like GaP clusters

2004 ◽  
Vol 854 ◽  
Author(s):  
Giuliano Malloci ◽  
Giancarlo Cappellini ◽  
Giacomo Mulas ◽  
Guido Satta
Keyword(s):  
Optical Absorption ◽  
Absorption Spectra ◽  
Density Functional ◽  
Electronic Excitations ◽  
Optical Absorption Spectra ◽  
Functional Theory ◽  
Quasi Particle ◽  
New Class ◽  
Excitonic Effects ◽  
Homo Lumo

ABSTRACTWe present quasi-particle (QP) corrections to the electronic energies for small GaP fullerenes, a new class of nanoscaled materials predicted to be stable and to show spontaneous formation. Using Time-Dependent Density Functional Theory we also computed the optical absorption spectra. The comparison between single-particle and optical absorption spectra yields strong excitonic effects with bonding energy up to 3.5 eV. The QP corrected HOMO-LUMO energy gaps confirm the high stability predicted for such molecules using ground-state computational schemes. The present results can be useful to identify the successful synthesis of these systems via optical absorption and QP spectra.

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 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.

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