scholarly journals The structural, elastic and optical properties of ScM (M = Rh, Cu, Ag, Hg) intermetallic compounds under pressure by ab initio simulations

2016 ◽  
Vol 05 (04) ◽  
pp. 1650024 ◽  
Author(s):  
Md. Lokman Ali ◽  
Md. Zahidur Rahaman ◽  
Md. Atikur Rahman
Keyword(s):  
Optical Properties ◽  
Ab Initio ◽  
Elastic Constants ◽  
Energy Region ◽  
Density Functional ◽  
Mechanical Stability ◽  
Computer Code ◽  
High Energy ◽  
High Energy Region ◽  
Generalized Gradient

The influence of pressure on the structural and elastic properties of ScM ([Formula: see text], Cu, Ag, Hg) compounds has been investigated by using ab initio approach pseudopotential plane-wave method based on the density functional theory within the generalized gradient approximation (GGA). The optical properties have been investigated under zero pressure. It is found that the optimized lattice parameters for all metals are in good agreement with the experimental data and other available theoretical values. We obtained three independent elastic constants [Formula: see text] ([Formula: see text] and [Formula: see text]) and various elastic parameters such as bulk modulus [Formula: see text], shear modulus [Formula: see text], Young’s modulus [Formula: see text], Poisson’s ratio [Formula: see text] and anisotropy factor [Formula: see text] as a function of pressure. In addition, the mechanical stability and ductile/brittle nature are also investigated from the calculated elastic constants. The study of optical properties reveals that all of these compounds possess good absorption coefficient in the high energy region and the refractive index of all these compounds is higher in the low energy region and gradually decreased in the high energy region. All these calculations have been carried out using the CASTEP computer code.

Computer Simulation of the Magnesium Silicide Polymorphs

2012 ◽  
Vol 170-173 ◽  
pp. 3312-3315
Author(s):  
Dong Chen ◽  
Chao Xu
Keyword(s):  
Optical Properties ◽  
Energy Region ◽  
High Performance ◽  
Density Functional ◽  
High Energy ◽  
Magnesium Silicide ◽  
High Energy Region ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Pseudo Potential

The anti-cotunnite magnesium silicide was constructed, and its absorption coefficient, dielectric function and loss function have been investigated through the plane-wave pseudo- potential calculations based on the density functional theory. In our scheme, we consider the Mg2Si crystal without defects or cracks. Significant features have been observed for the optical properties in the low-energy region and the high-energy region. The main focus of this paper is to determine the high-pressure optical properties of Mg2Si and find out if this material can be used as high-performance thermoelectric devices.

First-principles study of optical properties in Ca-doped ZnO alloys

Open Physics ◽  
2012 ◽  
Vol 10 (5) ◽  
Author(s):  
Li-Na Bai ◽  
Jian-She Lian ◽  
Wei-Tao Zheng ◽  
Qing Jiang
Keyword(s):  
Optical Properties ◽  
First Principles ◽  
Density Functional ◽  
Optical Transition ◽  
High Energy ◽  
Ternary Alloys ◽  
Potential Candidate ◽  
Coulomb Interactions ◽  
Generalized Gradient ◽  
Light Emitters

AbstractVarious electronic and optical properties of Zn1−x CaxO ternary alloys of wurtzite structure are calculated using a first-principles approach based on the framework of the generalized gradient approximation to density-functional theory. In particular, on-site Coulomb interactions are introduced, which can reasonably well predict the electronic properties and band gaps of the Zn1−x CaxO (0≤x≤0.25) system. The imaginary part of the calculated dielectric function indicates that the optical transition between O 2p states in the valence band and Zn 4s states in the conduction band shifts to the high-energy range as the Ca concentration increases. The calculated band gap shows a significant increase with increasing Ca concentration. Therefore, Zn1−x CaxO ternary alloys may be a potential candidate alloy for optoelectronic materials, and especially for light-emitters and detectors.

Ab Initio Study of Elastic Properties in Fe3Al-based Alloys

2008 ◽  
Vol 1128 ◽  
Author(s):  
Martin Friák ◽  
Johannes Deges ◽  
Frank Stein ◽  
Martin Palm ◽  
Georg Frommeyer ◽  
...  
Keyword(s):  
Ab Initio ◽  
Elastic Constants ◽  
Density Functional ◽  
Elevated Temperatures ◽  
Elastic Stiffness ◽  
Ternary Alloys ◽  
Elastic Response ◽  
Basic Material ◽  
Martensitic Steels ◽  
Generalized Gradient

AbstractFe3Al-based alloys constitute a very promising class of intermetallics with great potential for substituting austenitic- and martensitic steels at elevated temperatures. A wider use of these materials is partly hampered by their moderate ductility at ambient temperatures. Theoretical ab initio based calculations are becoming increasingly useful to materials scientists interested in designing new alloys. Such calculations are nowadays able to accurately predict basic material properties by needing only the atomic composition of the material. We have therefore employed this approach to explore (i) the relation between chemical composition and elastic constants, as well as (ii) the effect transition-metal substituents (Ti, W, V, Cr, Si) have on this relation. Using a scale-bridging approach we model the integral elastic response of Fe3Al-based polycrystals employing a combination of (i) single crystal elastic stiffness data determined by parameter-free first-principles calculations in combination with (ii) Hershey's homogenization model. The ab initio calculations employ density-functional theory (DFT) and the generalized gradient approximation (GGA). The thus determined elastic constants have been used to calculate the ratio between the bulk B and shear G moduli as an indication of brittle/ductile behavior. Based on this approach we have explored chemical trends in order to tailor mechanical properties. Using this information we have cast a selected set of Fe3Al-based ternary alloys, obtained for these the elastic constants by performing impulse excitation measurements at room as well as liquid nitrogen temperature and compared them with our theoretical results.

Optical Properties of LaB6: A Computer Aided Simulation

2012 ◽  
Vol 571 ◽  
pp. 292-295
Author(s):  
Ben Hai Yu ◽  
Chao Xu ◽  
Dong Chen
Keyword(s):  
Optical Properties ◽  
Dielectric Function ◽  
Density Functional ◽  
Mechanical Stability ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Lattice Constants ◽  
The Density Functional Theory ◽  
Theoretical Results ◽  
Good Agreement

We report ab initio calculations of the structural, elastic and optical properties of the compound LaB6 as a function of pressure. The computation is based on the density functional theory in combination with the generalized gradient approximation functional. The calculated lattice constants and elastic moduli are compared with the theoretical results and a good agreement is found. LaB6 can retain its mechanical stability in the pressure range of 0-20GPa. Besides, the frequency-dependent dielectric function, absorption coefficient and loss function of LaB6 are also obtained. The calculated static dielectric function is 8.8 at 0GPa and 5GPa. The computed results should be testified by experiments.

scholarly journals The Physical Properties of ThCr2Si2- Type Co-based Compound SrCo2Si2: An ab-initio Study

2021 ◽  
pp. 50-59
Keyword(s):  
Fermi Level ◽  
Density Functional ◽  
Mechanical Stability ◽  
High Energy ◽  
High Energy Region ◽  
Coating Materials ◽  
Functional Theory ◽  
Anisotropic Constant ◽  
The Density Functional Theory ◽  
Energy Package

In this article, we have studied the mechanical, electronic, and optical features of ThCr2Si2- type compound SrCo2Si2. The investigation has been done by using the first-principles method depend on the density functional theory (DFT) and the calculations were completed with the Cambridge Serial Total Energy Package (CASTEP) code. The optimized lattice parameters are well in accord with the existing synthesized values. The investigated elastic constants for this compound are positive which ensured the mechanical stability of this phase. The calculated values of Pugh’s ratio and Poisson’s ratio ensure the brittle character of SrCo2Si2. The universal anisotropic constant AU ensures the anisotropic behavior of SrCo2Si2.The softness nature of SrCo2Si2 is confirmed by the bulk modulus calculations. The overlapping of the valence band and conduction band near the Fermi level indicates the metallic nature of SrCo2Si2. At the Fermi level, the major contribution comes from Co-3d and Si-3p states. The large reflectivity in the high-energy region indicates that this compound might be useful as coating materials for reducing solar heating. The photoconductivity and absorption begins with zero photon energy which also ensures the metallic nature of SrCo2Si2.

Ab initio calculation on the Optical Properties of AA- Stacked two dimensional Graphene, Silicene, Germanene, and Stanene

2018 ◽  
Vol 1 (1) ◽  
pp. 46-50
Author(s):  
Rita John ◽  
Benita Merlin
Keyword(s):  
Optical Properties ◽  
Band Structure ◽  
Density Functional ◽  
Electronic Band Structure ◽  
Complex Refractive Index ◽  
Single Layer ◽  
Generalized Gradient ◽  
Electronic Band ◽  
Wide Range ◽  
Optical Region

In this study, we have analyzed the electronic band structure and optical properties of AA-stacked bilayer graphene and its 2D analogues and compared the results with single layers. The calculations have been done using Density Functional Theory with Generalized Gradient Approximation as exchange correlation potential as in CASTEP. The study on electronic band structure shows the splitting of valence and conduction bands. A band gap of 0.342eV in graphene and an infinitesimally small gap in other 2D materials are generated. Similar to a single layer, AA-stacked bilayer materials also exhibit excellent optical properties throughout the optical region from infrared to ultraviolet. Optical properties are studied along both parallel (||) and perpendicular ( ) polarization directions. The complex dielectric function (ε) and the complex refractive index (N) are calculated. The calculated values of ε and N enable us to analyze optical absorption, reflectivity, conductivity, and the electron loss function. Inferences from the study of optical properties are presented. In general the optical properties are found to be enhanced compared to its corresponding single layer. The further study brings out greater inferences towards their direct application in the optical industry through a wide range of the optical spectrum.

scholarly journals Analysis of Shielding Performance of Radiation-Shielding Materials According to Particle Size and Clustering Effects

2021 ◽  
Vol 11 (9) ◽  
pp. 4010
Author(s):  
Seon-Chil Kim
Keyword(s):  
Particle Size ◽  
Polymer Material ◽  
Energy Region ◽  
High Energy ◽  
Radiation Shielding ◽  
High Energy Region ◽  
Particle Structure ◽  
Effect Of Particle Size ◽  
Extensive Body ◽  
Shielding Material

In the field of medical radiation shielding, there is an extensive body of research on process technologies for ecofriendly shielding materials that could replace lead. In particular, the particle size and arrangement of the shielding material when blended with a polymer material affect shielding performance. In this study, we observed how the particle size of the shielding material affects shielding performance. Performance and particle structure were observed for every shielding sheet, which were fabricated by mixing microparticles and nanoparticles with a polymer material using the same process. We observed that the smaller the particle size was, the higher both the clustering and shielding effects in the high-energy region. Thus, shielding performance can be improved. In the low-dose region, the effect of particle size on shielding performance was insignificant. Moreover, the shielding sheet in which nanoparticles and microsized particles were mixed showed similar performance to that of the shielding sheet containing only microsized particles. Findings indicate that, when fabricating a shielding sheet using a polymer material, the smaller the particles in the high-energy region are, the better the shielding performance is. However, in the low-energy region, the effect of the particles is insignificant.

Study of thermo-elastic and lattice dynamics properties of half-Heusler compounds XMgAl (X = Li, Na) by computational investigations

2019 ◽  
Vol 33 (08) ◽  
pp. 1950093 ◽  
Author(s):  
A. Afaq ◽  
Abu Bakar ◽  
M. Rizwan ◽  
M. Aftab Fareed ◽  
H. Bushra Munir ◽  
...  
Keyword(s):  
Debye Temperature ◽  
Elastic Constants ◽  
Density Functional ◽  
Phonon Dispersion ◽  
Dynamic Properties ◽  
Mechanical Parameters ◽  
Heusler Compounds ◽  
Generalized Gradient ◽  
Text Type ◽  
Quantum Espresso

In this study, thermo-elastic and lattice dynamic properties of XMgAl (X = Li, Na) half-Heusler compounds are investigated using density functional theory implemented in WIEN2k and Quantum ESPRESSO codes. Generalized gradient approximation (GGA) as an exchange correlation function has been used in Kohn–Sham equations. Firstly, the structure of these Heusler compounds is optimized and then these optimized parameters are used to find three elastic constants [Formula: see text], [Formula: see text] and [Formula: see text] for [Formula: see text] type structures. Three elastic constants are then used to determine different elastic moduli like bulk modulus, shear modulus, Young’s modulus and other mechanical parameters like Pugh’s ratio, Poisson’s ratio, anisotropic ratio, sound velocities, Debye temperature and melting temperature. On behalf of these mechanical parameters, the brittle/ductile nature and isotropic/anisotropic behavior of the materials has been studied. Different regions of vibrational modes in the materials are also discussed on behalf of Debye temperature calculations. The vibrational properties of the half-Heusler compounds are computed using Martins–Troullier pseudo potentials implemented in Quantum ESPRESSO. The phonon dispersion curves and phonon density of states in first Brillion zone are obtained and discussed. Reststrahlen band of LiMgAl is found greater than NaMgAl.

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