Papers by Shahram Yalameha
arXiv (Cornell University), Feb 24, 2023
Physica Scripta
The bi-alkali pnictogens have attracted significant attention for optoelectronic and photocathodi... more The bi-alkali pnictogens have attracted significant attention for optoelectronic and photocathodic device applications. However, in most of the compounds belonging to this family, there has been less effort put into investigating the mechanical properties and topological phase transitions (TPT) of the compounds. Here, in the framework of density functional theory, the mechanical properties and topological phase transition of NaLi2Bi under hydrostatic pressures are investigated. Elastic constants and phonon calculations have shown the mechanical and dynamical stability of this compound under hydrostatic tension and compression. The analysis of the elastic constants show that the NaLi2Bi in the equilibrium state is an auxetic material with a negative Poisson’s ratio of -0.285, which changes to a material with a positive Poisson’s ratio under hydrostatic tension. Meanwhile, Poisson’s ratio and Pugh ratio indicate that this compound has brittle behavior and maintains it under hydrostati...
Physical Chemistry Chemical Physics
New first-principles calculations show that TiNI monolayer, once thought to be a 2D topological i... more New first-principles calculations show that TiNI monolayer, once thought to be a 2D topological insulator, has a trivial bandgap and is unstable under strain, highlighting the importance of accurate computations in studying topological materials.
Materials Science and Engineering: B
Journal of Physics: Condensed Matter, 2021
We report the topological phase and thermoelectric properties of bialkali bismuthide compounds (N... more We report the topological phase and thermoelectric properties of bialkali bismuthide compounds (Na, K)2RbBi, as yet hypothetical. The topological phase transitions of these compounds under hydrostatic pressure are investigated. The calculated topological surface states and Z 2 topological index confirm the nontrivial topological phase. The electronic properties and transport coefficients are obtained using the density functional theory combined with the Boltzmann transport equation. The relaxation times are determined using the deformation potential theory to calculate the electronic thermal and electrical conductivity. The calculated mode Grüneisen parameters are substantial, indicating strong anharmonic acoustic phonons scattering, which results in an exceptionally low lattice thermal conductivity. These compounds also have a favorable power factor leading to a relatively flat p-type figure-of-merit over a broad temperature range. Furthermore, the mechanical properties and phonon ...
Computational Condensed Matter, 2018
Abstract Based on density functional theory, the structural and elastic properties of InSb1-xBix ... more Abstract Based on density functional theory, the structural and elastic properties of InSb1-xBix alloys have been studied using first principle calculations. The generalized gradient approximation in the presence of spin-orbit coupling is utilized to perform the calculations presented in this paper. The calculated lattice constants of InSb1-xBix alloys are in good agreement with the available experimental data. The mechanical stability of these alloys is demonstrated using elastic constants. The ductility and brittleness of these alloys are investigated using both Poisson's ratio and Pugh's ratio. Moreover, the anisotropy of InSb1-xBix alloys is studied using the universal index and the 3D representation of Young's modulus. According to the obtained values of Poisson's ratio, the InSb0.5Bi0.5 and InBi alloys are auxetic materials.
International Journal of Modern Physics B, 2018
In this paper, thermodynamic and elastic properties of the AlNi and AlNi3 were investigated using... more In this paper, thermodynamic and elastic properties of the AlNi and AlNi3 were investigated using density functional theory (DFT). The full-potential linearized augmented plane-wave (APW) in the framework of the generalized gradient approximation as used as implemented in the Wien2k package. The temperature dependence of thermal expansion coefficient, bulk modulus and heat capacity in a wide range of temperature (0–1600 K) were investigated. The calculated elastic properties of the compounds show that both intermetallic compounds of AlNi and AlNi3 have surprisingly negative Poisson’s ratio (NPR). The results were compared with other experimental and computational data.
Physics Letters A, 2019
Abstract First principle calculations have been employed to investigate the effects of Y concentr... more Abstract First principle calculations have been employed to investigate the effects of Y concentration, pressure and temperature on various properties of Gd 1 − x Y x AuPb ( x = 0 , 0.25 , 0.5 , 0.75 , 1 ) alloys using density functional theory (DFT). The full potential linearized augmented plane wave (FP-LAPW) method within a framework of the generalized gradient approximation (GGA) is used to perform the calculated results of this paper. Phase stability of Gd 1 − x Y x AuPb alloys is studied using the total energy versus unit cell volume calculations. The equilibrium lattice parameters of these alloys are in good agreement with the available experimental results. The mechanical stability of Gd 1 − x Y x AuPb alloys is proved using elastic constants calculations. Also, the influence of Y concentration on elastic properties of Gd 1 − x Y x AuPb alloys such as Young's modulus, shear modulus, Poisson's ratio and anisotropy factor are investigated and analyzed. By considering both Pugh's ratio and Poisson's ratio, the ductility and brittleness of these alloys are studied. In addition, the total density of states and orbital's hybridizations of different atoms are investigated and discussed. Moreover, the effect of pressure and temperature on some important thermodynamic properties is investigated.
Journal of Magnetism and Magnetic Materials, 2018
Abstract Topological insulators are novel state of quantum matter that have a bulk band gap like ... more Abstract Topological insulators are novel state of quantum matter that have a bulk band gap like an ordinary insulator, but have protected conducting states by time reversal symmetry on their edge or surface. The spin-orbit coupling can play an important role in these materials, resulting in a band inversion at time reversal invariant momenta (TRIM) points. The topological phase and the effect of the hydrostatic pressure on the electronic structure and topological phase of the KNa2Sb compound are investigated by using both first-principles calculations and ab-initio based tight-binding computations. Under hydrostatic lattice strain until 5.6%, the KNa2Sb compound is semimetal with zero energy band gap and has an inverted band order. In this pressure, the Z2 invariants of this compound are calculated using the parity analysis at TRIM points and evolution of wannier charge centers at the six TRIM plane. The calculated surface states at (0 0 1) surface show a single Dirac cone exists on the X ¯ Γ ¯ W ¯ line at the surface Brillouin zone. To investigate the stability of KNa2Sb compound the phonon dispersions and elastic tensors of this compound in the cubic structure are calculated.
Journal of Computational Electronics
First-principles electronic, thermoelectric, thermodynamic, and optical calculations of an alkali... more First-principles electronic, thermoelectric, thermodynamic, and optical calculations of an alkali pnictide compound, Li 3 Bi, are implemented by WIEN2k, BoltzTraP and Gibbs2 using density functional theory in the presence of spin-orbit coupling. The generalized gradient approximation and modified Becke and Janson functionals with the generalized gradient approximation are utilized for the treatment of exchange and correlation potential. The Li 3 Bi electronic band structure indicates that this compound is a semiconductor at zero pressure. The energy band gap of this compound closes at a pressure of 6.0 GPa. In contrast, low pressures enhance the energy band gap and reduce the band width of the valence and conduction bands. The pressure and temperature effects on the thermoelectric and thermodynamic performance of this compound are investigated. This results reveal (1) an increase in the power factor values under high temperatures and low pressures, (2) a reduction in the thermal expansion and the specific heat capacity at constant volume and an increase in the Debye temperature under high pressures at constant temperature. Also, the evaluation of optical properties under various hydrostatic pressures shows an increase in the static real part of the dielectric function and the static reflectivity of Li 3 Bi at a pressure of 6 GPa.
Journal of Magnetism and Magnetic Materials, 2020
Based on ab initio calculations, we have studied structural, electronic and optical properties of... more Based on ab initio calculations, we have studied structural, electronic and optical properties of MoX2(X = S, Se) metal dichalcogenides and their nano-layers (NLs) according to the density functional theory using Wien2k code. The generalized gradient approximation (GGA) and GGA Engel-vosko are adopted to perform the exchange-correlation calculations. The equilibrium lattice parameters of MoS2 and MoSe2 compounds are calculated. The mechanical stability of these compounds is proved using Born condition. Moreover, the ductility and brittleness of MoX2 compounds are studied. The topological phase of MoS2 and MoSe2 bulks and their NLs is studied utilizing band order, Z2 invariant and surface density of states. The optical properties of MoX2 bulks and NLs are studied. The Penn model is satisfied for both MoS2 and MoSe2 compounds by studying their real part of static dielectric function. The increase of the thickness of these NLs leads to the changes in the absorption, reflectivity and en...
We introduce a computational method and a user-friendly code with a terminalbased graphical user ... more We introduce a computational method and a user-friendly code with a terminalbased graphical user interface (GUI), named ElATools, developed to analyze mechanical and anisotropic elastic properties. ElATools enables facile analysis of the second-order elastic stiffness tensor of two-dimensional (2D) and three-dimensional (3D) crystal systems. It computes and displays the main mechanical properties including the bulk modulus, Young’s modulus, shear modulus, hardness, p-wave modulus, universal anisotropy index, Chung-Buessem anisotropy index, log-Euclidean anisotropy parameter, Cauchy pressures, Poisson’s ratio, and Pugh’s ratio, using three averaging schemes of Voigt, Reuss, and Hill. It includes an online and offline database from the Materials Project with more than 13,000 elastic stiffness constants for 3D materials. The program supports output files of the well-known computational codes IRelast, IRelast2D, ElaStic, and AELAS. Four types of plotting and visualization tools are inte...
Computer Physics Communications
Nanomaterials
Using first-principles calculations, we predict highly stable cubic bialkali bismuthides Cs(Na, K... more Using first-principles calculations, we predict highly stable cubic bialkali bismuthides Cs(Na, K)2Bi with several technologically important mechanical and anisotropic elastic properties. We investigate the mechanical and anisotropic elastic properties under hydrostatic tension and compression. At zero pressure, CsK2Bi is characterized by elastic anisotropy with maximum and minimum stiffness along the directions of [111] and [100], respectively. Unlike CsK2Bi, CsNa2Bi exhibits almost isotropic elastic behavior at zero pressure. We found that hydrostatic tension and compression change the isotropic and anisotropic mechanical responses of these compounds. Moreover, the auxetic nature of the CsK2Bi compound is tunable under pressure. This compound transforms into a material with a positive Poisson’s ratio under hydrostatic compression, while it holds a large negative Poisson’s ratio of about −0.45 along the [111] direction under hydrostatic tension. An auxetic nature is not observed in...
Materials Science and Engineering: R: Reports
Materials Science and Engineering: B
Physica E: Low-dimensional Systems and Nanostructures
Uploads
Papers by Shahram Yalameha