Local-Field and Exchange-Correlation Effects in Optical Spectra of Wide-Band–Gap Semiconductors

1996 ◽  
Vol 423 ◽  
Author(s):  
V. I. Gavrilenko ◽  
F. Bechstedt
Keyword(s):  
Local Field ◽  
Density Functional ◽  
Random Phase ◽  
Wide Band ◽  
Optical Spectra ◽  
Wide Band Gap ◽  
Functional Theory ◽  
Exchange Correlation ◽  
The Density Functional Theory ◽  
Wide Band Gap Semiconductors

AbstractThe density-functional theory with ab initio pseudopotentials has been used to study the linear optical response of semiconductors. We present results for optical spectra where the effects of the macroscopic local-field and microscopic exchange-correlation interaction are included beyond diagonal and random-phase approximation. Quasiparticle corrections to the single-particle energies have been added in the polarization function. Numerical calculations are performed for the column-IV materials Si, SiC, and diamond as model substances.

First Principles Modelling of Scroll-to-Nanotube Defect: Screw-Type Dislocation

2006 ◽  
Vol 527-529 ◽  
pp. 1583-1586 ◽  
Author(s):  
I. Suarez-Martinez ◽  
G. Savini ◽  
M.I. Heggie
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Wide Band ◽  
Interlayer Spacing ◽  
Density Functional Theory Study ◽  
Wide Band Gap ◽  
Functional Theory ◽  
Potential Applications ◽  
Wide Band Gap Semiconductors ◽  
Type Dislocation

Carbon nanotubes present interesting potential applications especially in nanoelectronics. Their electrical properties are known to be a function of their chirality. It happens that 1/3 of CNs are metallic and 2/3 are semiconductors. Narrow nanotubes are expected to be wide-band gap semiconductors. Several experimental results have shown that the thickness of a multi-wall nanotube along the axis can change, while the interlayer spacing remains fairly constant. These observations suggest the coexistence in the same tube of a scroll structure and a multi-wall nested tube. We explain this defect as a screw dislocation which by gliding transforms between these two forms. In this paper, we present a density functional theory study of the structure and energetics of screw dislocations in AA and ABC graphite, and we discuss their role in the scroll-to-nanotube transformation in multi-wall nanotubes.

MAGNETIC MAP OF MnNi ALLOYED MONOLAYER ON Cu(001) SUBSTRATE: AB-INITIO CALCULATIONS

2010 ◽  
Vol 09 (06) ◽  
pp. 619-622
Author(s):  
BOTHINA A. HAMAD
Keyword(s):  
Density Functional ◽  
Theoretical Study ◽  
Magnetic Moments ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Exchange Correlation ◽  
Generalized Gradient Approximation ◽  
Exchange Correlation Potential ◽  
The Density Functional Theory ◽  
Correlation Potential

In this work, a theoretical study of the structural, electronic and magnetic properties are presented for Mn 0.5 Ni 0.5 alloyed overlayer adsorbed on Cu (001) surface. The calculations were performed using the density functional theory (DFT) and the exchange-correlation potential was treated by the generalized gradient approximation (GGA). The system was fully relaxed except for the central layer, which yields to outward relaxations and inward Mn and Ni surface atoms, respectively in the ferromagnetic and antiferromagnetic configurations. The in-plane ferromagnetic configuration was found to be more stable than the antiferromagnetic one by 25 meV/atom. The local magnetic moments of Mn atoms were found to be about 4 μ B , whereas those of the Ni atoms where found to be 0.46 μ B .

Electronic Transport Properties of SiC Nanotube with Antisite Defect

2011 ◽  
Vol 110-116 ◽  
pp. 5495-5499
Author(s):  
Jiu Xu Song ◽  
Hong Xia Liu
Keyword(s):  
Transport Properties ◽  
Electronic Transport ◽  
Density Functional ◽  
Wide Band ◽  
Antisite Defect ◽  
Wide Band Gap ◽  
Functional Theory ◽  
Electronic Transport Properties ◽  
Current Voltage ◽  
Sic Nanotube

The electronic transport properties of an (8, 0) SiC nanotube (SiCNT) with antisite defect are investigated with the method combined non-equilibrium Green’s function with density functional theory, in which the defect is formed with a carbon atom being substituted by a silicon atom. In transmission spectrum of the nanotube, a transmission valley about 1.68 eV near the Fermi energy is discovered, which indicates that the nanotube is a wide band-gap semiconductor. In its current-voltage characteristic, turn-on voltages of ±1.0 V are found under positive and negative bias. This originates from more orbital participating in its electronic transport properties caused by the bias. These results are meaningful to investigations on working mechanisms of SiCNT electronic devices.

scholarly journals Linear response of partially ionized, dense plasmas

1992 ◽  
Vol 10 (2) ◽  
pp. 299-309 ◽  
Author(s):  
T. Błeński ◽  
B. Cichocki
Keyword(s):  
Cluster Expansion ◽  
Density Functional ◽  
Random Phase ◽  
Functional Theory ◽  
New Formalism ◽  
Dense Plasmas ◽  
The Density Functional Theory ◽  
Partially Ionized Plasmas ◽  
Final Cluster ◽  
Partially Ionized

We propose a new formalism to electronic polarizability of dense, partially ionized plasmas. This formalism is based upon the density functional theory for the electronic equilibrium, the random phase approximation for the density response of electrons, and the cluster expansion in the averaging over ionic configurations. The first term in the final cluster expansion for the imaginary part of electron polarizability corresponds to the Lindhard dielectric function formula. The second term contains the electronic states of the average atom. The additional effects that result from this theory are: channel mixing (screening), “inverse Bremstrahlung” corrections, and free-bound electronic transitions. Our approach allows the plasma (collective) and atomic physics phenomena to be treated in the frame of one formalism. The theory can be applied for stopping power and opacity calculations.

scholarly journals Structural and piezoelectric coefficients of AlP under pressure

2018 ◽  
Vol 6 (2) ◽  
pp. 53
Author(s):  
Salah Daoud ◽  
Rabie Mezouar ◽  
Abdelfateh Benmakhlouf
Keyword(s):  
Density Functional ◽  
Structural Parameters ◽  
Generalized Gradient ◽  
Aluminum Phosphide ◽  
Functional Theory ◽  
Exchange Correlation ◽  
Generalized Gradient Approximation ◽  
Zinc Blende ◽  
Density Functional Perturbation Theory ◽  
The Density Functional Theory

The present work aims to investigate the structural parameters and the piezoelectric coefficients of cubic zinc-blende Aluminum phosphide (AlP) under high pressure up to 21 GPa, using plane wave-pseudopotential (PW-PP) approach in the framework of the density functional theory (DFT) and the density functional perturbation theory (DFPT) with the generalized gradient approximation (GGA) for the exchange-correlation functional. The results obtained are analyzed and compared with other data of the literature. The structural parameters and the piezoelectric coefficients calculated here agree well with other data of the literature. We found also that both the direct and converse piezoelectric coefficients increase with increasing pressure up to 21 GPa. 

Theoretical Analysis of the DOS and Band Structural Properties of Ti1-XSnxO2 Solid Solutions

2012 ◽  
Vol 465 ◽  
pp. 33-36
Author(s):  
Zhi Dong Lin ◽  
Wen Long Song ◽  
Ju Cheng Zheng
Keyword(s):  
Band Gap ◽  
Solid Solutions ◽  
Density Functional ◽  
Wide Band ◽  
Low Energy ◽  
Low Density ◽  
First Principle ◽  
Wide Band Gap ◽  
Functional Theory ◽  
First Principle Calculations

The band structure and density of states (DOS) of Ti1-xSnxO2 solid solutions with x=0, 1/8, 1/4, 1/2 and 1 were investigated by means of the first-principle calculations based on density functional theory. The result indicated that band gap and Fermi level of TiO2-SnO2 vary continuously from those of pure TiO2 to those of Sn content increasing. In addition, the DOS moves towards low energy and the bang gap is broadened with growing value of x. The wide band gap and the low density of the states in the conduction band result in the enhancement of photoactivity in Ti1-xSnxO2.

Effects of Zinc Cations Doping and the Photo-Absorbed Mechanism for NaTaO3 Nanoparticles

2012 ◽  
Vol 519 ◽  
pp. 244-247
Author(s):  
Yu Ze Xie ◽  
Yu Lu Liu ◽  
Xiao Jing Wang
Keyword(s):  
Valence Band ◽  
Density Functional ◽  
Light Response ◽  
Wide Band ◽  
Wide Band Gap ◽  
Functional Theory ◽  
Intermediate Band ◽  
Lower Energy Region ◽  
Recombination Centers ◽  
Zinc Cations

Effects of zinc cations doping into wide band gap semiconductor photocatalysts of electronic structure, visible light response, and photo-absorbed mechanism were studied. A series of Zn-doped NaTaO3 catalysts were prepared by hydrothermal method. XRD results suggested that zinc were successfully doped into the NaTaO3 nanocrystal in the Zn2+ ions state. UV-vis diffuse reflectance spectra indicated no obvious red-shift was observed in the series of zinc doped NaTaO3 photo-catalysts. The simulation of energy band structure by density functional theory unfolded that d orbital of Zn2+ is lower than the Ta 5d and also O 2p orbital, thus it located at the lower energy region of the valence band. Therefore the substitution of Ta5+ ions by Zn2+ ions can not form an intermediate band (IB) between the top of the valence band (VB) and the bottom of conduct band. Meanwhile Zn species can become the recombination centers of photoinduced electrons and holes. Thus, the quickly recombination of e--h+ pairs is one of the most significant factors which deteriorate the photoactivity of Zn-doped NaTaO3

scholarly journals Ab Initio Study of MgTe Self-Interstitial (Mgi and Tei): A Wide Band Gap Semiconductor

2017 ◽  
Vol 16 ◽  
pp. 47-51
Author(s):  
Emmanuel Igumbor ◽  
Ezekiel Omotoso ◽  
Walter Ernst Meyer
Keyword(s):  
Band Gap ◽  
Density Functional ◽  
Defect Formation ◽  
Local Density ◽  
Wide Band ◽  
Shallow Donor ◽  
Generalized Gradient ◽  
Wide Band Gap ◽  
Functional Theory ◽  
Formation Energies

We present results of defect formation energies and charge state thermodynamic transition levels of Mg and Te interstitials in MgTe wurzite structure. We use the generalized gradient approximation and local density approximation functionals in the framework of density functional theory for all calculations. The formation energies of the Mg and Te interstitials in MgTe for both the tetrahedral and hexagonal configurations were obtained. The Mg and Te interstitials in MgTe depending on the functional, introduced transition state levels that are either donor or acceptor within the band gap of the MgTe. The Te interstitial exhibit charge states controlled metastability, negative-U and DX centre properties. The Mg interstitial acts as deep or shallow donor and there is no evidence of acceptor levels found for the Mg interstitial.

Sign in / Sign up

Export Citation Format

Share Document