scholarly journals Composition Dependence of Electronic, Elastic, and Polarization Properties of Wurtzite InxGa1-xN and CdxZn1-xO Ternary Alloys

2021 ◽  
Author(s):  
Abdesamed BENBEDRA ◽  
Said MESKINE ◽  
Hamza ABBASSA ◽  
El Habib ABBES ◽  
Abdelkader BOUKORTT
Keyword(s):  
Electric Fields ◽  
Density Functional ◽  
Composition Dependence ◽  
Alloy Composition ◽  
Density Functional Theory Calculations ◽  
Electric Polarization ◽  
Ternary Alloys ◽  
Linear Behavior ◽  
Vegard’S Law ◽  
Total Polarization

Abstract We report the results of density functional theory calculations of several properties of wurtzite-structured InGaN and CdZnO alloys. It is shown that the investigated properties, including the internal parameter, bandgap, mechanical moduli, and electric polarization are nonlinear functions of alloy composition, as they deviate from the linear behavior predicted by Vegard’s law. Based on these results, InGaN and CdZnO are materials whose properties can be tuned via In and Cd concentrations. The spontaneous and piezoelectric polarizations considerably affect the properties of alloys-based devices due to the huge electric fields that build up at the heteroineterfaces. In this work we propose a method of controlling such fields by employing the composition dependence of the total polarization. We support this proposal by showing that, in the case of InGaN, an optimal alloy composition can be found that effectively reduces the polarization-induced electric fields, thereby improving the efficiency of optoelectronic applications.

scholarly journals Demystifying the Soai Reaction

2019 ◽  
Author(s):  
Soumitra Athavale ◽  
Adam Simon ◽  
Kendall N. Houk ◽  
Scott Denmark
Keyword(s):  
Density Functional ◽  
Spectroscopic Analysis ◽  
Chiral Symmetry Breaking ◽  
Kinetic Studies ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Group Transfer ◽  
Linear Behavior ◽  
Structural Mutations ◽  
Soai Reaction

The extraordinary Soai reaction has profoundly impacted chemists’ perspective of chiral symmetry breaking, absolute asymmetric synthesis and its role in the origin of biological homochirality. Herein, we describe the unprecedented observation of asymmetry amplifying autocatalysis in the alkylation of 5-(trimethylsilylethynyl)pyridine-3-carbaldehyde using diisopropylzinc. Kinetic studies with a “Trojan-horse” substrate and spectroscopic analysis of a series of zinc-alkoxides that incorporate specific structural mutations reveal a ‘pyridine-assisted cube escape’. The new cluster functions as a catalyst that activates the ‘floor-to-floor’ bound aldehyde and poises a coordinated diisopropylzinc moiety for alkyl group transfer. Transitionstate models leading to both the homochiral and heterochiral products were validated by density functional theory calculations. Moreover, experimental and computational analysis of the heterochiral complex provides a definitive explanation for the non-linear behavior of this system. Our deconstruction of the Soai system contributes substantially to understanding the mechanism of this transformation that has stood as a longstanding challenge in chemistry.<br>

Exceptional mechano-electronic properties in the HfN2 monolayer: a promising candidate in low-power flexible electronics, memory devices and photocatalysis

2020 ◽  
Vol 22 (37) ◽  
pp. 21275-21287 ◽  
Author(s):  
Manish Kumar Mohanta ◽  
I. S. Fathima ◽  
Abir De Sarkar
Keyword(s):  
Density Functional Theory ◽  
Low Power ◽  
Electronic Properties ◽  
Electric Fields ◽  
Flexible Electronics ◽  
Density Functional ◽  
External Perturbation ◽  
Density Functional Theory Calculations ◽  
Promising Candidate ◽  
Functional Theory

The response of the electronic properties of the HfN2 monolayer to external perturbation such as strain and electric fields has been investigated using density functional theory calculations for its device-based applications and photocatalysis.

Ab intio Investigations of Lattice Parameters in ZnMgO Alloys

2009 ◽  
Vol 1201 ◽  
Author(s):  
Markus Heinemann ◽  
Marcel Giar ◽  
Christian Heiliger
Keyword(s):  
Density Functional ◽  
Local Density ◽  
Density Functional Theory Calculations ◽  
Lattice Parameters ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Lattice Constants ◽  
Exchange Correlation ◽  
Vegard’S Law ◽  
Constant Unit

AbstractWe perform density functional theory calculations to determine equilibrium lattice parameters of wurtzite Zn1-xMgxO alloys for Mg concentrations x ranging from 0 to 31.25 %. We use the local density approximation (LDA) as well as the generalized gradient approximation (GGA) for the exchange correlation functional. For the lattice constants a and c we find a deviation from Vegard's law and a constant unit cell volume independent of the Mg concentration.

scholarly journals Strategies for Red-Shifting Type I Photoinitiators: Internal Electric Fields versus Lewis Acids versus Increasing Conjugation

2019 ◽  
Vol 72 (8) ◽  
pp. 627 ◽  
Author(s):  
Nicholas S. Hill ◽  
Michelle L. Coote
Keyword(s):  
Excited States ◽  
Electric Fields ◽  
Lewis Acids ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Water Soluble ◽  
Type I ◽  
Internal Electric Field ◽  
Functional Theory ◽  
Derivatives Of

Time-dependent density functional theory calculations were performed on derivatives of Irgacure 2959, a water-soluble, acetophenone-type photoinitiator, in order to assess the relative merits and drawbacks of three distinct ways of modifying its photochemistry: Lewis acid complexation, changing the amount of conjugation in the molecule, and application of an internal electric field through inclusion of a remote charged functional group. The effectiveness of each of the three methods was evaluated against the magnitude of the change in energy of the excited states. Internal electric fields were shown to provide the best method for targeting specific excited states in a controlled and rational manner. The other strategies also had significant effects but it was more difficult to independently target different transitions. Nonetheless, for the specific case of Irgacure 2959, we predict that its complexation with Mg2+ ions in a range of solvents will both red-shift the initiator’s absorbance while improving its efficiency and it is thus a promising candidate for testing as a visible light photoinitiator.

First-principles calculations of structural, electronic and thermal properties of Zn1−x MgxS ternary alloys

Open Physics ◽  
2014 ◽  
Vol 12 (1) ◽  
Author(s):  
Samia Lamraoui ◽  
Rachid Bensalem ◽  
Khadidja Hacini ◽  
Hocine Meradji ◽  
Sebti Ghemid ◽  
...  
Keyword(s):  
Thermal Properties ◽  
Density Functional ◽  
Small Deviation ◽  
Experimental Studies ◽  
Theoretical Data ◽  
Debye Model ◽  
Ternary Alloys ◽  
Full Potential ◽  
Generalized Gradient ◽  
Vegard’S Law

AbstractStructural, electronic and thermal properties of Zn1−x MgxS ternary alloys are studied by using the full potential-linearized augmented plane wave method (FP-LAPW) within the density functional theory (DFT). The Wu-Cohen generalized gradient approximation (WC-GGA) is used in this approach for the exchangecorrelation potential. Moreover, the modified Becke-Johnson approximation (mBJ) is adopted for band structure calculations. The dependence of the lattice constant, bulk modulus and band gap on the composition x showed that the first exhibits a small deviation from the Vegard’s law, whereas, a marginal deviation of the second from linear concentration dependence (LCD). The bowing of the fundamental gap versus composition predicted by our calculations agrees well with the available theoretical data. The microscopic origins of the gap bowing are explained by using the approach of Zunger and co-workers. Thermal effects on some macroscopic properties of Zn1−x MgxS alloys are also investigated using the quasi-harmonic Debye model, in which the phononic effects are considered. As, this is the first quantitative theoretical prediction of the thermal properties of Zn1−x MgxS alloys, no other calculated results and furthermore no experimental studies are available for comparison.

Phase Transitions on Gan Surfaces

2002 ◽  
Vol 743 ◽  
Author(s):  
C. Adelmann ◽  
L. Lymperakis ◽  
J. Brault ◽  
G. Mula ◽  
J. Neugebauer ◽  
...  
Keyword(s):  
Experimental Data ◽  
Phase Diagram ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Rate Equations ◽  
Arrhenius Behavior ◽  
Adsorption Phase ◽  
Linear Behavior ◽  
Principle Density Functional Theory ◽  
Simple Growth

ABSTRACTRecent experimental and theoretical studies highlighted the importance of the growing surface structure on the final morphology of GaN. Actually, optimum morphology is achieved by growth in presence of a Ga bilayer adsorbed on the GaN surface. The threshold fluxes limiting the region of the Ga bilayer adsorption have been measured as a function of the GaN substrate temperature, giving rise to a Ga adsorption phase diagram. The Ga flux limiting the regions in the adsorption phase diagram exhibit a linear behavior in an Arrhenius plot. However, both energy activation (about 5 eV) and prefactor (in the 1025 range) are surprinsingly high. These questions were adressed by studying the adsorption/desorption of Ga adatoms and small islands (consisting of 2 and 3 Ga adatoms) on the Ga bilayer surface employing first principle density functional theory calculations. We find a desorption barrier of 2.1 eV and a binding energy between two Ga atoms of approximately 0.3 eV. Using these numbers we derived a simple growth model (based on rate equations). An analysis of the experimental data with the model revealed the origin of the large difference in the activation energies and the unusually large prefactor. We find that the nucleation of the droplets cannot be described by a simple Arrhenius behavior (as commonly assumed to fit experimental data) but that the nucleation energy is temperature dependent.

scholarly journals Demystifying the Soai Reaction

2019 ◽  
Author(s):  
Soumitra Athavale ◽  
Adam Simon ◽  
Kendall N. Houk ◽  
Scott Denmark
Keyword(s):  
Density Functional ◽  
Spectroscopic Analysis ◽  
Chiral Symmetry Breaking ◽  
Kinetic Studies ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Group Transfer ◽  
Linear Behavior ◽  
Structural Mutations ◽  
Soai Reaction

The extraordinary Soai reaction has profoundly impacted chemists’ perspective of chiral symmetry breaking, absolute asymmetric synthesis and its role in the origin of biological homochirality. Herein, we describe the unprecedented observation of asymmetry amplifying autocatalysis in the alkylation of 5-(trimethylsilylethynyl)pyridine-3-carbaldehyde using diisopropylzinc. Kinetic studies with a “Trojan-horse” substrate and spectroscopic analysis of a series of zinc-alkoxides that incorporate specific structural mutations reveal a ‘pyridine-assisted cube escape’. The new cluster functions as a catalyst that activates the ‘floor-to-floor’ bound aldehyde and poises a coordinated diisopropylzinc moiety for alkyl group transfer. Transitionstate models leading to both the homochiral and heterochiral products were validated by density functional theory calculations. Moreover, experimental and computational analysis of the heterochiral complex provides a definitive explanation for the non-linear behavior of this system. Our deconstruction of the Soai system contributes substantially to understanding the mechanism of this transformation that has stood as a longstanding challenge in chemistry.<br>

ENERGY BAND-GAPS OF MgxZn1-xSe: VIOLATION OF VEGARD'S LAW

2004 ◽  
Vol 18 (01) ◽  
pp. 137-142 ◽  
Author(s):  
Z. CHARIFI ◽  
H. BAAZIZ ◽  
N. BOUARISSA
Keyword(s):  
Energy Band ◽  
Composition Dependence ◽  
Composition Range ◽  
Band Gaps ◽  
Ternary Alloys ◽  
Lattice Constants ◽  
Bowing Parameter ◽  
Zinc Blende ◽  
System Transition ◽  
Vegard’S Law

Based on a pseudopotential scheme, the composition dependence of energy band-gaps of zinc-blende Mg x Zn 1-x Se ternary alloys in the composition range of 0≤x≤1 are determined. The effect of deviation of lattice constants of the alloys of interest from Vegard's law on the optical bowing parameter and system transition between the direct and indirect structures is discussed.

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