A Theoretical Study of Dislocation Formation at Surfaces in Covalent Materials: Effect of Step Geometry and Reactivity

2005 ◽  
Vol 108-109 ◽  
pp. 193-198
Author(s):  
Sandrine Brochard ◽  
Julien Godet ◽  
Laurent Pizzagalli ◽  
Pierre Beauchamp ◽  
José Soler
Keyword(s):  
First Principles ◽  
Theoretical Study ◽  
Quantitative Agreement ◽  
First Principles Calculation ◽  
Atomistic Simulations ◽  
Near Surface ◽  
Empirical Potential ◽  
Qualitative And Quantitative ◽  
Surface Steps ◽  
Semi Empirical

Atomistic simulations using both semi-empirical potential and first principles calculation have been performed to study the initiation of plasticity near surface steps in silicon. A comparison of both techniques on a prototypic case shows qualitative and quantitative agreement. Then each method has been used to analyze in detail some characteristics of the surface step: the step geometry thanks to semi-empirical potential calculations, and the step reactivity with ab initio techniques.

scholarly journals Strain Conditions for the Inverse Heusler Type Fully Compensated Spin-Gapless Semiconductor Ti2MnAl: A First-Principles Study

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2091 ◽  
Author(s):  
Tie Yang ◽  
Liyu Hao ◽  
Rabah Khenata ◽  
Xiaotian Wang
Keyword(s):  
Thermodynamic Properties ◽  
First Principles ◽  
Density Functional ◽  
Theoretical Study ◽  
Debye Model ◽  
Pressure Effects ◽  
First Principles Calculation ◽  
Strain Condition ◽  
Functional Theory ◽  
Future Work

In this work, we systematically studied the structural, electronic, magnetic, mechanical and thermodynamic properties of the fully compensated spin-gapless inverse Heusler Ti2MnAl compound under pressure strain condition by applying the first-principles calculation based on density functional theory and the quasi-harmonic Debye model. The obtained structural, electronic and magnetic behaviors without pressure are well consistent with previous studies. It is found that the spin-gapless characteristic is destroyed at 20 GPa and then restored with further increase in pressure. While, the fully compensated ferromagnetism shows a better resistance against the pressure up to 30 GPa and then becomes to non-magnetism at higher pressure. Tetragonal distortion has also been investigated and it is found the spin-gapless property is only destroyed when c/a is less than 1 at 95% volume. Three independent elastic constants and various moduli have been calculated and they all show increasing tendency with pressure increase. Additionally, the pressure effects on the thermodynamic properties under different temperature have been studied, including the normalized volume, thermal expansion coefficient, heat capacity at constant volume, Grüneisen constant and Debye temperature. Overall, this theoretical study presents a detailed analysis of the physical properties’ variation under strain condition from different aspects on Ti2MnAl and, thus, can provide a helpful reference for the future work and even inspire some new studies and lead to some insight on the application of this material.

CFD Study of an Autonomous Submarine in Extraterrestrial Seas

2017 ◽  
Author(s):  
S. Carberry Mogan ◽  
P. Sawicki ◽  
C. J. Bernardo ◽  
D. Chen ◽  
I. Sahin ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Computational Study ◽  
Liquid Hydrocarbon ◽  
Quantitative Agreement ◽  
Near Surface ◽  
Surface Conditions ◽  
Qualitative And Quantitative

A computational study is conducted to evaluate the performance of an extraterrestrial submarine operating in the liquid hydrocarbon seas of Saturn’s largest moon, Titan. To simulate the flow around the submarine and offer a prediction for thrust and power requirements, Computational Fluid Dynamics tools, ANSYS© FLUENT© and DualSPHysics, are utilized for the deeply submerged and near-surface conditions, respectively. Several operational scenarios are investigated and comparisons are made with other available results with a good qualitative and quantitative agreement.

Theoretical Study of N Incorporation Effect during SiC Oxidation

2013 ◽  
Vol 740-742 ◽  
pp. 455-458 ◽  
Author(s):  
Shigenori Kato ◽  
Kenta Chokawa ◽  
Katsumasa Kamaiya ◽  
Kenji Shiraishi
Keyword(s):  
First Principles ◽  
Theoretical Study ◽  
Oxidation Process ◽  
The Other ◽  
No Oxidation ◽  
First Principles Calculation ◽  
Interface Properties ◽  
Covalent Bonds ◽  
State Generation ◽  
N Incorporation

We investigated the atomistic mechanism of N incorporation during SiC oxidation by the first principles calculation. We found that N atoms play two characteristic roles in NO oxidation of SiC surface. One is that N atoms tend to form three-fold coordinated covalent bonds on a SiC(0001) surface, which assist the termination of surface dangling bonds, leading to improve the interface properties. The other is that N atoms form N-N bond like a double bond. The N2 molecule is desorbed from SiC surface, which do not disturb the oxidation process of SiC surfaces. These results indicate that N incorporation is effective to suppress defect state generation at SiO2/SiC interfaces during SiC oxidation.

Resistance simulations for junctions of SW and MW carbon nanotubes with various metal substrates

Open Physics ◽  
2011 ◽  
Vol 9 (2) ◽  
Author(s):  
Yuri Shunin ◽  
Yuri Zhukovskii ◽  
Natalia Burlutskaya ◽  
Stefano Bellucci
Keyword(s):  
Carbon Nanotubes ◽  
First Principles ◽  
Theoretical Study ◽  
Metal Contacts ◽  
Metallic Elements ◽  
Adequate Description ◽  
Cluster Approach ◽  
Effective Media ◽  
Semi Empirical ◽  
Ballistic Conductivity

AbstractThis theoretical study focuses on junctions between the carbon nanotubes (CNTs) and contacting metallic elements of a nanocircuit. Numerical simulations on the conductance and resistance of these contacts have been performed using the multiple scattering theory and the effective media cluster approach. Two models for CNT-metal contacts have been considered in this paper: a) first principles “liquid metal” model and b) semi-empirical model of “effective bonds” based on Landauer notions on ballistic conductivity. Within the latter, which is a more adequate description of chirality effects, we have simulated both single-wall (SW) and multi-wall (MW) CNTs with different morphology. Results of calculations on resistance for different CNT-Me contacts look quantitatively realistic (from several to hundreds kOhm, depending on chirality, diameter and thickness of MW CNT). The inter-wall transparency coefficient for MW CNT has been also simulated, as an indicator of possible ‘radial current’ losses.

Prediction on structural, mechanical and thermal properties of Al4SiC4, Al4C3 and 4H-SiC under high pressure by first-principles calculation

2017 ◽  
Vol 31 (09) ◽  
pp. 1750080 ◽  
Author(s):  
Liang Sun ◽  
Yimin Gao ◽  
Katsumi Yoshida ◽  
Toyohiko Yano ◽  
Wen Wang
Keyword(s):  
Thermal Properties ◽  
First Principles ◽  
Elastic Moduli ◽  
Theoretical Study ◽  
Lattice Parameter ◽  
First Principles Calculation ◽  
Mechanical And Thermal Properties ◽  
Text Data ◽  
Cell Structures ◽  
Higher Temperature

A theoretical study is conducted by first-principles theory to study the structural, electronic, elastic and thermal properties of Al4SiC4, Al4C3 and 4H-SiC phases under pressure. The calculated results indicated that the volumetric shrinkage of Al4SiC4 declines to 16% compared with 4H-SiC for 12% and its length of lattice parameter along c-axis decreases faster than that of along other axes in cell structures. The mechanical properties of Al4SiC4 like elastic constants and elastic moduli increase continuously under pressure. The thermal expansion coefficient of three compounds under pressure are studied first. When temperature is lower than 500 K, the coefficient increases rapidly first then gradually tends to a linear accession at higher temperature and the propensity of increment becomes moderate. The [Formula: see text] data decreases slightly with pressure but increases dramatically with temperature for all compounds.

A THEORETICAL STUDY OF BISTABILITY OF POLYDIACETYLENE: TCDU(poly(5,7-dodecadiyne-1,12-diyl-bis-phenylurethane)

2001 ◽  
Vol 15 (28n30) ◽  
pp. 3821-3824
Author(s):  
HIDEKI KATAGIRI ◽  
YUKIHIRO SHIMOI ◽  
SHUJI ABE
Keyword(s):  
Potential Energy ◽  
First Principles ◽  
Theoretical Study ◽  
Geometry Optimization ◽  
Optimization Procedure ◽  
Stable Structure ◽  
Type Structure ◽  
Potential Energy Curves ◽  
First Principles Calculation ◽  
Bond Lengths

We performed a first-principles calculation of typical polydiacetylene (PDA), TCDU (poly(5,7-dodecadiyne-1,12-diyl-bis-phenylurethane)). Potential energy curves (PEC's) as a function of two bond lengths of the backbone chain are presented. The present PEC's show that TCDU has only an acetylene-type stable structure and a butatriene-type structure is unstable, consistent with our previous calculations with a geometry optimization procedure. This result is in contrast to the case of a hypothetical hydrogen-substituted PDA where a butatriene-type structure is obtained as a meta-stable structure.

FIRST PRINCIPLES CALCULATION OF THE PHONON SPECTRA OF SOLIDS

1981 ◽  
Vol 42 (C6) ◽  
pp. C6-625-C6-627 ◽  
Author(s):  
P. E. Van Camp ◽  
V. E. Van Doren ◽  
J. T. Devreese
Keyword(s):  
First Principles ◽  
First Principles Calculation ◽  
Phonon Spectra
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