scholarly journals Ab initioStudies of Electronic Structure of Defects in PbTe

2005 ◽  
Vol 864 ◽  
Author(s):  
Salameh Ahmad ◽  
Daniel Bilc ◽  
S.D. Mahanti ◽  
M.G. Kanatzidis
Keyword(s):  
Electronic Structure ◽  
Valence Band ◽  
Conduction Band ◽  
Density Of States ◽  
Resonance State ◽  
Interesting Case ◽  
The Other ◽  
Defect States ◽  
Strong Resonance ◽  
Structure Calculations

AbstractAb initioelectronics structure calculations have been carried out in a series of RPb2n-1Te2n, n=16, compounds to understand the nature of “defect” states introduced by R where R = vacancy, monovalent Na, K, Rb, Cs, Ag atoms and divalent Cd atoms. We find that the density of states (DOS) near the top of the valence band and the bottom of the conduction band get significantly modified. The Na atom seems to perturb this region least (ideal acceptor in PbTe) and the other monovalent atoms enhance the DOS near the top of the valence band. Cd is an interesting case, since it introduces a strong resonance state near the bottom of the conduction band.

Electronic Structure of Defects in SnTe

2013 ◽  
Vol 701 ◽  
pp. 125-130
Author(s):  
Salameh Ahmad
Keyword(s):  
Electronic Structure ◽  
Band Gap ◽  
Valence Band ◽  
Fundamental Difference ◽  
Density Of State ◽  
Defect States ◽  
Deep Defect ◽  
Conduction Bands ◽  
Resonant States ◽  
Structure Calculations

Myab initioelectronic structure calculations inRSn2n-1Te2n, n=16, R = a vacancy, Cd, and In show that when Sn atom is substituted by R, the Density of State (DOS) of the valence and conduction bands get strongly perturbed. There are significant changes near the band gap region. Sn vacancy causes very little change near the bottom of the conduction band DOS whereas there is an increase in the DOS near the top of the valence band. Results for In impurity shows that, unlike PbTe, the deep defect states in SnTe are resonant states near the top of the valence band. In PbTe these deep defect states lie in the band-gap region (act asn-type). This fundamental difference in the position of the deep defect states in SnTe and PbTe explains the experimental anomalies seen in the case of In impurities (act asn-type in PbTe andp-type in SnTe).

scholarly journals CALCULATION OF ELECTRONIC STRUCTURE OF 2D NaAu INTERMETALLIC LAYERS

2021 ◽  
pp. 475-482
Author(s):  
Юрий Александрович Кузнецов ◽  
Михаил Николаевич Лапушкин
Keyword(s):  
Electronic Structure ◽  
Intermetallic Compound ◽  
Band Gap ◽  
Valence Band ◽  
Conduction Band ◽  
Density Of States ◽  
Intermetallic Layers

Проведен расчет плотности состояний различной толщины 2D -слоев интерметаллида NaAu. 2D -слоев интерметаллида NaAu моделировались суперячейки NaAu (111) 2 х 2 х 2. Для монослойного 2D -слоя интерметаллида NaAu установлено наличие запрещенной зоны с шириной 1,87 эВ. Увеличение толщины толщины 2D -слоев интерметаллида NaAu до двух монослоев показал уменьшение ширины запрещенной зоны до 0,81эВ. Дальнейшее увеличение толщины 2D -слоев интерметаллида NaAu приводит к исчезновению запрещенной зоны, что указывает на переход полупроводник - металл для 2D -слоя интерметаллида NaAu толщиной три монослоя. Валентная зона 2D -слоя интерметаллида NaAu сформирована в основном Au 5d электронами, с незначительным вкладом Au 6s и Au 6p электронов. Зона проводимости NaAu образована в основном Au 6р электронами с незначительным вкладом электронов Na 3 s . The calculation of the density of states of various thicknesses of the 2D -layers of the intermetallic compound has been carried out. 2D -layers of intermetallic compound NaAu are simulated by supercells NaAu (111) 2 x 2 x 2. For a monolayer 2D -layer of an intermetallic compound NaAu the presence of a bandgap with a width of 1,87 eV has been established. An increase in the thickness of the 2D -layers of the intermetallic compound NaAu to two monolayers showed a decrease in the bandgap to 0,81 eV. A further increase in the thickness of the 2D -layers of the intermetallic compound NaAu leads to the disappearance of the band gap, which indicates a semiconductor-metal transition for the 2D -layer of the intermetallic compound NaAu with a thickness of three monolayers. The valence band of the 2D -layer of the intermetallic compound NaAu is formed mainly by Au 5d electrons, with an insignificant contribution from Au 6s and Au 6p electrons. The conduction band of NaAu is formed mainly by Au 6p electrons with an insignificant contribution of electrons Na 3s .

First-principle calculation of the electronic structure, DOS and effective mass TlInSe2

2017 ◽  
Vol 31 (14) ◽  
pp. 1750155 ◽  
Author(s):  
N. A. Ismayilova ◽  
G. S. Orudzhev ◽  
S. H. Jabarov
Keyword(s):  
Electronic Structure ◽  
Effective Mass ◽  
Valence Band ◽  
Conduction Band ◽  
Density Of States ◽  
Valence Band Maximum ◽  
First Principle ◽  
Band Maximum ◽  
Effective Masses ◽  
Structure Density

The electronic structure, density of states (DOS), effective mass are calculated for tetragonal TlInSe2 from first principle in the framework of density functional theory (DFT). The electronic structure of TlInSe2 has been investigated by Quantum Wise within GGA. The calculated band structure by Hartwigsen–Goedecker–Hutter (HGH) pseudopotentials (psp) shows both the valence band maximum and conduction band minimum located at the T point of the Brillouin zone. Valence band maximum at the T point and the surrounding parts originate mainly from 6s states of univalent Tl ions. Bottom of the conduction band is due to the contribution of 6p-states of Tl and 5s-states of In atoms. Calculated DOS effective mass for holes and electrons are [Formula: see text], [Formula: see text], respectively. Electron effective masses are fairly isotropic, while the hole effective masses show strong anisotropy. The calculated electronic structure, density of states and DOS effective masses of TlInSe2 are in good agreement with existing theoretical and experimental results.

A STUDY ON STRAIN AFFECTING ELECTRONIC STRUCTURE OF WURTZITE ZnO BY FIRST PRINCIPLES

2009 ◽  
Vol 23 (19) ◽  
pp. 2339-2352 ◽  
Author(s):  
LI BIN SHI ◽  
SHUANG CHENG ◽  
RONG BING LI ◽  
LI KANG ◽  
JIAN WEI JIN ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Electronic Structure ◽  
Band Structure ◽  
Valence Band ◽  
Density Of States ◽  
First Principles ◽  
Density Functional ◽  
Functional Theory ◽  
Electron Density Difference ◽  
Different Strains

Density of states and band structure of wurtzite ZnO are calculated by the CASTEP program based on density functional theory and plane-wave pseudopotential method. The calculations are carried out in axial and unaxial strains, respectively. The results of density of states in different strains show that the bottom of the conduction band is always dominated by Zn 4s, and the top of valence band is always dominated by O 2p. The variation of the band gap calculated from band structure is also discussed. In addition, p-d repulsion is used in investigating the variation of the top of the valence band in different strains and the results can be verified by electron density difference.

Bulk and Surface Electronic Structure of GaN Measured Using Angle-Resolved Photoemission, Soft X-ray Emission and Soft X-ray Absorption

1996 ◽  
Vol 449 ◽  
Author(s):  
Kevin E. Smith ◽  
Sarnjeet S Dhesi ◽  
Laurent-C. Duda ◽  
Cristian B Stagarescu ◽  
J. H. Guo ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Valence Band ◽  
Absorption Spectra ◽  
Conduction Band ◽  
Brillouin Zone ◽  
Emission Spectra ◽  
Partial Density ◽  
High Symmetry ◽  
X Ray ◽  
X Ray Absorption

ABSTRACTThe electronic structure of thin film wurtzite GaN has been studied using a combination of angle resolved photoemission, soft x-ray absorption and soft x-ray emission spectroscopies. We have measured the bulk valence and conduction band partial density of states by recording Ga L- and N K- x-ray emission and absorption spectra. We compare the x-ray spectra to a recent ab initio calculation and find good overall agreement. The x-ray emission spectra reveal that the top of the valence band is dominated by N 2p states, while the x-ray absorption spectra show the bottom of the conduction band as a mixture of Ga 4s and N 2p states, again in good agreement with theory. However, due to strong dipole selection rules we can also identify weak hybridization between Ga 4s- and N 2p-states in the valence band. Furthermore, a component to the N K-emission appears at approximately 19.5 eV below the valence band maximum and can be identified as due to hybridization between N 2p and Ga 3d states. We report preliminary results of a study of the full dispersion of the bulk valence band states along high symmetry directions of the bulk Brillouin zone as measured using angle resolved photoemission. Finally, we tentatively identify a non-dispersive state at the top of the valence band in parts of the Brillouin zone as a surface state.

The electronic structure of disordered system

1964 ◽  
Vol 279 (1376) ◽  
pp. 82-97 ◽  
Keyword(s):  
Electronic Structure ◽  
Band Structure ◽  
Density Of States ◽  
Disordered System ◽  
Perfect Lattice ◽  
Geometric Approximation ◽  
Band Structure Calculations ◽  
Interacting Electrons ◽  
Simplifying Assumptions ◽  
Structure Calculations

A general expression is written down for the density of states of non-interacting electrons in a disordered system. The expression is obtained on the basis of two simplifying assumptions; the geometric approximation, which is connected with the disorder, and an approximation concerning the potential which is commonly used in band structure calculations. In the case of a perfect lattice the result of Kohn & Rostoker (1954) for the band structure of the lattice is derived, and details of the density of states are available from the formula thus obtained. It is shown how the change in the energy of the electrons due to the presence of a phonon can be obtained.

Electronic States in the Gap of a-Si from Bond Angle Variations

1990 ◽  
Vol 192 ◽  
Author(s):  
B. N. Davidson ◽  
G. Lucovsky
Keyword(s):  
Valence Band ◽  
Density Of States ◽  
Bond Angle ◽  
Bethe Lattice ◽  
Band Edge ◽  
Conduction Band Edge ◽  
Valence Band Edge ◽  
Defect States ◽  
Discrete State ◽  
Bond Angles

ABSTRACTWe investigate the formation of defect states in the gap of a-Si arising from deviations from the ideal tetrahedral bond angles. The local density of states for Si atoms in disordered environments is calculated using tight-binding parameters for the cluster-Bethe lattice method. The Hamiltonian for a-Si with bond angle distortions is taken as an average over many configurations associated with a random choice of bond angles, weighted by Gaussian distributions with standard deviations between 2°.and 10°. Bond angle deviations in this range generate a density of defect states at the valence band edge that: 1) increases as the average bond angle deviation increases; and 2) is significantly larger than the density of band tail states generated at the conduction band edge. We obtain a shift of the absorption edge from the joint density of states (DOS) as a function of bond angle deviations. In addition, a calculation of the DOS for a distorted tetrahedral cluster embedded in an idealized Bethe lattice yields a threshold bond angle distortion of ±20° for the appearance of a discrete state in the gap near the valence band edge.

First-Principles Calculations on the Electronic Structure of ZnO Nanowires

2012 ◽  
Vol 198-199 ◽  
pp. 23-27
Author(s):  
Nan Zhang ◽  
Hong Sheng Zhao ◽  
Dong Yang ◽  
Wen Jie Yan
Keyword(s):  
Electronic Structure ◽  
Band Gap ◽  
Valence Band ◽  
Conduction Band ◽  
First Principles ◽  
Density Functional ◽  
Valence Band Maximum ◽  
Zno Nanowires ◽  
Cross Sectional ◽  
Quantum Size

Based upon the density functional theory (DFT) in this paper, the first-principles approach is used to study the electronic structure of different cross-sectional diameters of ZnO [0001] nanowires of wurtzite structure. The results show that ZnO [0001] nanowires have a wide direct band gap. Located in the G-point of the Brillouin zone the conduction band minimum and valence band maximum are relatively smooth. The conduction band is mainly composed of Zn 4s and Zn 4p states, and the valence band is composed of Zn 3d and O 2p states. The effective mass of conduction band electrons and valence band holes are large while their mobility is very low which show that conductive ability of pure defect-free [0001] ZnO nanowires is weak. Along with the increase of the cross-sectional diameters, the band gap gradually decreases that indicates quantum size effects are obvious in the nano size range.

ELECTRONIC STRUCTURE CALCULATIONS FOR MoSe2 USING EXTENDED HUCKEL TIGHT-BINDING METHOD

2004 ◽  
Vol 18 (01) ◽  
pp. 35-44 ◽  
Author(s):  
DONALD H. GALVAN
Keyword(s):  
Electronic Structure ◽  
Density Of States ◽  
Population Analysis ◽  
Tight Binding ◽  
Electronic Structure Calculations ◽  
Total Density ◽  
Mulliken Population Analysis ◽  
Energy Bands ◽  
Mulliken Population ◽  
Structure Calculations

To gain insight into the electronic properties of MoSe 2 (molybdenum selenide, also known as drysdallite), electronic structure calculations, total and projected density of states, crystal orbital overlap population and Mulliken population analysis were performed. The calculated energy bands depict a semiconductor behavior with a direct gap (at K) of 0.91 eV and an indirect gap (from Γ to K) of 3.6 eV, respectively. Total and projected density of states provided information about the contribution from each orbital of each atom to the total density of states. Moreover, the bonding strength between some atoms within the unit cell was obtained. Mulliken population analysis corroborates the electron filling of the Mo dz2 orbitals in agreement with another experimental and theoretical results.

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