scholarly journals Critical Evaluation of Various Spontaneous Polarization Models and Induced Electric Fields in III-Nitride Multi-Quantum Wells

Materials ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 4935
Author(s):  
Ashfaq Ahmad ◽  
Pawel Strak ◽  
Kamil Koronski ◽  
Pawel Kempisty ◽  
Konrad Sakowski ◽  
...  
Keyword(s):  
Ab Initio Calculations ◽  
Quantum Wells ◽  
Ab Initio ◽  
Electric Fields ◽  
Spontaneous Polarization ◽  
Berry Phase ◽  
Critical Evaluation ◽  
Theoretical Data ◽  
Polarization Difference ◽  
Binary Compounds

In this paper, ab initio calculations are used to determine polarization difference in zinc blende (ZB), hexagonal (H) and wurtzite (WZ) AlN-GaN and GaN-InN superlattices. It is shown that a polarization difference exists between WZ nitride compounds, while for H and ZB lattices the results are consistent with zero polarization difference. It is therefore proven that the difference in Berry phase spontaneous polarization for bulk nitrides (AlN, GaN and InN) obtained by Bernardini et al. and Dreyer et al. was not caused by the different reference phase. These models provided absolute values of the polarization that differed by more than one order of magnitude for the same material, but they provided similar polarization differences between binary compounds, which agree also with our ab initio calculations. In multi-quantum wells (MQWs), the electric fields are generated by the well-barrier polarization difference; hence, the calculated electric fields are similar for the three models, both for GaN/AlN and InN/GaN structures. Including piezoelectric effect, which can account for 50% of the total polarization difference, these theoretical data are in satisfactory agreement with photoluminescence measurements in GaN/AlN MQWs. Therefore, the three models considered above are equivalent in the treatment of III-nitride MQWs and can be equally used for the description of the electric properties of active layers in nitride-based optoelectronic devices.

scholarly journals Geometric and Energetic Data from Ab Initio Calculations of Haloethene, Haloimine, Halomethylphosphine, Haloiminophosphine, Halodiazene, Halodiphosphene and Halocyclopropane

2019 ◽  
Author(s):  
Kridtin Chinsukserm ◽  
Wanutcha Lorpaiboon ◽  
Peerayar Teeraniramitr ◽  
Taweetham Limpanuparb
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Quantum Chemical ◽  
Theoretical Data ◽  
Geometric Optimization ◽  
Basis Set ◽  
Halogenated Compounds ◽  
Wolfram Mathematica

<p>This article presents theoretical data on geometric and energetic features of halogenated compounds of cyclopropane (∆) and ethene (C=C), imine (C=N), methylphosphine (C=P), iminophosphine (N=P), diazene (N=N) and diphosphene (P=P). The data were obtained from <i>ab initio</i> geometric optimization and frequency calculations at HF, B3LYP, MP2 and CCSD levels of theory on 6-311++G(d,p) basis set. Input structures were generated by shell scripts and run by Q-Chem quantum chemical package. The output files were processed to extract geometric and energetic information by Wolfram Mathematica.</p>

scholarly journals Geometric and Energetic Data from Ab Initio Calculations of Haloethene, Haloimine, Halomethylphosphine, Haloiminophosphine, Halodiazene, Halodiphosphene and Halocyclopropane

2019 ◽  
Author(s):  
Kridtin Chinsukserm ◽  
Wanutcha Lorpaiboon ◽  
Peerayar Teeraniramitr ◽  
Taweetham Limpanuparb
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Quantum Chemical ◽  
Theoretical Data ◽  
Geometric Optimization ◽  
Basis Set ◽  
Halogenated Compounds ◽  
Wolfram Mathematica

<p>This article presents theoretical data on geometric and energetic features of halogenated compounds of cyclopropane (∆) and ethene (C=C), imine (C=N), methylphosphine (C=P), iminophosphine (N=P), diazene (N=N) and diphosphene (P=P). The data were obtained from <i>ab initio</i> geometric optimization and frequency calculations at HF, B3LYP, MP2 and CCSD levels of theory on 6-311++G(d,p) basis set. Input structures were generated by shell scripts and run by Q-Chem quantum chemical package. The output files were processed to extract geometric and energetic information by Wolfram Mathematica.</p>

scholarly journals Geometric and Energetic Data from Ab Initio Calculations of Haloethene, Haloimine, Halomethylphosphine, Haloiminophosphine, Halodiazene, Halodiphosphene and Halocyclopropane

2019 ◽  
Author(s):  
Kridtin Chinsukserm ◽  
Wanutcha Lorpaiboon ◽  
Peerayar Teeraniramitr ◽  
Taweetham Limpanuparb
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Quantum Chemical ◽  
Theoretical Data ◽  
Geometric Optimization ◽  
Basis Set ◽  
Halogenated Compounds ◽  
Wolfram Mathematica

<p>This article presents theoretical data on geometric and energetic features of halogenated compounds of cyclopropane (∆) and ethene (C=C), imine (C=N), methylphosphine (C=P), iminophosphine (N=P), diazene (N=N) and diphosphene (P=P). The data were obtained from <i>ab initio</i> geometric optimization and frequency calculations at HF, B3LYP, MP2 and CCSD levels of theory on 6-311++G(d,p) basis set. Input structures were generated by shell scripts and run by Q-Chem quantum chemical package. The output files were processed to extract geometric and energetic information by Wolfram Mathematica.</p>

scholarly journals Examination of permittivity for depolarization field of ferroelectric by ab initio calculation, suggesting hidden mechanisms

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yukio Watanabe
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Spontaneous Polarization ◽  
Ab Initio Calculation ◽  
Surface Effects ◽  
Atomic Scale ◽  
Free Standing ◽  
Unit Cells ◽  
Scale Surface

AbstractElectrostatics of depolarization field Ed in relation to the polarization is studied. In particular, the value of permittivity for Ed (εd) in prototypical situations of ferroelectrics, including Mehta formula, is examined by ab initio calculations. By using spontaneous polarization PS corresponding to accurate experiment ones, we show εd = 1, which suggests that the results of εd ≫ 1 indicate hidden mechanisms; εd = 1 suggests that the effect of Ed is significant to induce intriguing important phenomena overlooked by εd ≫ 1. A bridge between εd = 1 and εd ≫ 1, i.e. the consistency of εd = 1 with conventional results is presented. The exact electrostatic equality of head-to-head–tail-to-tail domains to free-standing ferroelectrics is deduced. Hence, most stoichiometric clean freestanding monodomain ferroelectrics and head-to-head–tail-to-tail domains are shown unstable regardless of size, unless partially metallic. This verifies the previous results in a transparent manner. This conclusion is shown consistent with a recent hyperferroelectric LiBeSb and “freestanding” monolayer ferroelectrics, of which origin is suggested to be adsorbates. In addition, this restriction is suggested to break in externally strained ultrathin ferroelectrics. The macroscopic formulas of Ed are found valid down to a several unit-cells, when electronic and atomic-scale surface effects are unimportant and accurate PS is used.

scholarly journals Critical Assessment of the Al-Ti-Zr System

2020 ◽  
Vol 41 (5) ◽  
pp. 687-701
Author(s):  
Z. Kahrobaee ◽  
M. Palm
Keyword(s):  
Phase Equilibria ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Phase Diagrams ◽  
Critical Evaluation ◽  
Critical Assessment ◽  
Isothermal Sections ◽  
Type Calculation ◽  
Zr Alloys

Abstract Only within the last couple of years, complete isothermal sections for the Al-Ti-Zr system have been determined. Up to then there had been several investigations, but these were limited to the Ti-Zr and Ti-Al sides and the Ti- and Al corners of the system. Also recently the system has been evaluated by thermodynamic ab initio calculations and CALPHAD-type (CALculation of PHAse Diagrams) modelling. As Al-Ti-Zr alloys are of interest for a variety of applications and as the last assessment has been performed more than 15 years ago, this new critical evaluation of the existing literature about phase equilibria in the Al-Ti-Zr system has been performed.

Millimetre-wave and infrared spectroscopy of Br13 CN: anharmonic force field of cyanogen bromide from spectroscopic data and ab initio calculations

1997 ◽  
Vol 90 (3) ◽  
pp. 495-497
Author(s):  
CLAUDIO ESPOSTI ◽  
FILIPPO TAMASSIA ◽  
CRISTINA PUZZARINI ◽  
RICCARDO TARRONI ◽  
ZDENEK ZELINGER
Keyword(s):  
Infrared Spectroscopy ◽  
Force Field ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Spectroscopic Data ◽  
Cyanogen Bromide ◽  
Millimetre Wave ◽  
Anharmonic Force
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