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Nanomaterials (20794991) 15(2)
The present work investigates the interfacial and atomic layer-dependent mechanical properties, SOC-entailing phonon band structure, and comprehensive electron-topological–elastic integration of ZrTe2 and NiTe2. The anisotropy of Young’s modulus, Poisson’s ratio, and shear modulus are analyzed using density functional theory with the TB-mBJ approximation. NiTe2 has higher mechanical property values and greater anisotropy than ZrTe2. Phonon dispersion analysis with SOC effects predicts the dynamic stability of both compounds. Thus, the current research unifies electronic band structure analysis, topological characterization, and elastic property calculation to reveal how these transition metal dichalcogenides are influenced by their structural, electronic, and mechanical properties. The results obtained in this work can be used in the further development of spintronic and nanoelectronic devices. © 2025 by the authors.
Materials Science and Engineering: B (09215107) 315
The structural, electronic, mechanical properties, and phonon dispersions of lithium-based intermetallic compounds Li2PdX (X = Ga, Ge, In), Li2InPt, Li2InAu, and LiPd3 are investigated using density functional theory (DFT) via the Wien2k code. Stability is analyzed through energy-volume curves, cohesive and formation energies, elastic tensor components, and phonon density of states. Hydrostatic pressure effects on stability and mechanical properties are also examined. The results confirm the stability of these compounds in nonmagnetic cubic phases, with calculated lattice parameters and bulk moduli in agreement with existing data, validating the computational approach. Phonon density of states analysis establishes the dynamical stability of Li2PdGa and Li2PdGe in space group Fm3¯m (No. 225); Li2InPt, Li2InAu, and Li2PdIn in F4¯3m (No. 216); and LiPd3 in Pm3¯m (No. 221). Elastic properties reveal a critical pressure point (Pt) beyond which mechanical instability occurs. Around Pt, Pugh's ratio (bulk-to-shear modulus ratio) exhibits limiting behavior, persisting as long as C44 is comparable to C11-C12. However, for LiPd3, a marked reduction in C44 near Pt eliminates this behavior, underscoring its distinct mechanical response. A derived limit for Pugh's ratio offers new insights into the elastic behavior of these materials under extreme conditions. Electronic properties, including the density of states and linear electronic specific heat coefficient, confirm the metallic nature of these compounds. These findings provide valuable insights into the pressure-dependent mechanical and electronic behavior of lithium-based intermetallic compounds, informing their potential applications in energy storage, electronic devices, and pressure-sensing. © 2025
Physical Chemistry Chemical Physics (14639084) 27(8)pp. 4407-4418
Two-dimensional (2D) materials have garnered significant attention for their exceptional potential in electronic, optical, and flexible nanodevices. In this study, we introduce a novel 2D In2F2 monolayer, revealed through first-principles calculations, and demonstrate its thermal, dynamic, and mechanical stability. Our findings show that the In2F2 monolayer exhibits notable anisotropic mechanical behavior, including auxetic properties characterized by a negative Poisson's ratio. Electronic band structure calculations, using both PBE-GGA and HSE06 functionals, indicate that this monolayer is a semiconductor with a small, nontrivial topological bandgap of approximately 1.58 meV. The observed s-p band inversion and calculated invariant, confirm the presence of a nontrivial topological phase in this material. Furthermore, the optical absorption spectrum reveals strong anisotropy, with significant absorption in the visible to near-infrared range along the y-axis, suggesting potential applications in polarized photodetectors and anisotropic optoelectronic devices. The relatively low work function (3.86 eV) further increases its suitability for electron-emission applications, such as thermionic devices. These mechanical, electronic, and optical properties position the In2F2 monolayer as a promising candidate for next-generation electronics, flexible electronics, and anisotropic optoelectronics. © 2025 The Royal Society of Chemistry.
Journal of Materials Science (15734803) 60(21)pp. 8749-8765
This study investigates the structural, electronic, and magnetic properties of XBr2, XI2, and XBrI (X = Mn, Co) compounds using density functional theory, incorporating spin–orbit coupling and the GGA + U framework. Cohesive and formation energy calculations reveal that MnBr2 is most stable in the ferromagnetic phase, while the other compounds favor antiferromagnetic ordering. The inclusion of the effective Coulomb screening potential (Ueff) enhances the localization of 3d orbitals, leading to increased magnetic moments. Electronic structure analyses show that most compounds transition to semiconducting behavior in the antiferromagnetic phase—except CoI2—while MnBr2, CoBr2, and CoI2 exhibit half-metallicity in the ferrimagnetic phase. In the antiferromagnetic phase, MnBr2, MnI2, and MnBrI display topological Dirac-like points between the R and Γ points, suggesting the presence of massless fermions and enabling phenomena such as the quantum Hall effect and ultra-high carrier mobility. The computational results are consistent with available experimental data, highlighting the potential of Mn- and Co-based van der Waals compounds for spintronic and quantum applications. © The Author(s) 2025.
Computational Condensed Matter (23522143) 39
In this study, the structural, elastic, vibrational, electronic, optical, thermodynamic, and thermoelectric properties of the chalcogenide ternary Y2ZnX4 (Y = In, Ga; X = S, Se) compounds are comprehensively investigated using the pseudopotential plane-wave (PP-PW) and full-potential linearized augmented plane wave (FP-LAPW) methods. The analysis of elastic and vibrational properties reveals the dynamic and mechanical stability of these compounds. The calculated energy band gaps, ranging from 1.47 eV (Ga2ZnSe4) to 2.55 eV (In2ZnS4) in the visible spectrum, decrease as X atoms are substituted with S to Se. All examined compounds demonstrate favorable optical absorption (α > 105 cm−1) in the ultraviolet region. Notably, Ga2ZnSe4 exhibits absorption red-shift towards the visible region at hν = 2.76 eV due to its lower energy band gap, making it a promising candidate for solar cells. The three-dimensional representation of Young's modulus indicates significant deviation from sphericity, revealing anisotropic behavior in all compounds. Pugh's ratio, Poisson's ratio, and Cauchy's pressure analysis suggest ductile behavior in all four chalcogenide ternary compounds. Additionally, all compounds, except In2ZnS4, display auxetic properties. Finally, the calculated thermoelectric properties identify Ga2ZnS4 and In2ZnS4 as promising candidates for high-performance thermoelectric applications, with high Seebeck coefficients of 1848 and 1936 μV/K, respectively, and ZT values approaching unit. © 2024 Elsevier B.V.
Journal of Materials Science (15734803) 59(36)pp. 17079-17095
This study presents a comprehensive analysis of the electronic, mechanical, and optical properties of CrxMo1-xS2, a bulk transition metal dichalcogenide. Using density functional theory with spin–orbit interaction, we employed both the generalized gradient approximation (GGA) and the modified Becke–Johnson potential (mBJ-GGA) to evaluate these properties. Our results confirm that all CrxMo1-xS2 alloys are nonmagnetic and thermodynamically stable, as evidenced by cohesive energy calculations. Mechanical assessments comply with Born’s criteria, further affirming their stability. Interestingly, lower concentrations of Cr, particularly in Cr0.125Mo0.875S2, significantly enhance atomic bond strength and elastic stiffness. Additional mechanical analysis, including the universal elastic anisotropy index, microhardness, machinability index, and Pugh’s criterion, reveals that all alloys are anisotropic and brittle, with Cr0.375Mo0.625S2 and Cr0.625Mo0.375S2 demonstrating superior machinability. On the electronic front, the addition of Cr substantially modifies the MoS2 bandgap and the density of states near the Fermi level. Even at low Cr concentrations, a significant reduction in the energy bandgap is observed, with notable contributions from Cr-dz2 orbitals to the valence and conduction bands. Optically, we examined the dielectric constant ε(ω) components, along with absorption (α(ω)), reflection (R(ω)), and refraction (n(ω)) coefficients in both X and Z directions. An increase in Cr concentration leads to a redshift in these properties, with prominent peaks in the visible light spectrum, especially in the yellow and blue light energies. The thorough examination of electronic, mechanical, and optical properties suggests that CrxMo1-xS2 alloys hold significant potential for various applications in electronic and optical technologies, particularly in areas requiring bandgap engineering. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2024.
Advanced Engineering Materials (14381656) 26(22)
In this computational study, density functional theory (DFT) is employed to analyze the structural, electronic, elastic, and topological properties of ternary compounds MXY (M = Ti, Sn, Ir, X = Se, Te, Y = Se, Te). The effects of spin–orbit interaction and pressure-induced strain are investigated to understand their influence on the stability, mechanical properties, and electronic behavior, paving the way for potential technological applications. The findings confirm that these compounds are inherently stable in nonmagnetic phases, with spin–orbit interaction critically influencing their energy–volume landscapes. The calculated lattice parameters, ratios of lattice constants, and bulk moduli closely align with existing data, confirming the reliability of our approach. Mechanical assessments reveal distinct behaviors: IrSe2 exhibits the highest stiffness due to pronounced covalent bonding, contrasting with SnTe2's elastic anisotropy and SnSeTe's nearly isotropic properties. Electronically, most compounds show metallic characteristics, except SnSe2, which behaves as a semiconductor with an indirect, pressure-sensitive energy bandgap. Topological analysis under varying hydrostatic pressures indicates band inversions in TiSe2, IrSe2, and SnSeTe, suggesting topological phase transitions absent in other compounds. This study enriches our understanding of these materials and refines the application of DFT in material design. © 2024 The Author(s). Advanced Engineering Materials published by Wiley-VCH GmbH.
Materials Chemistry and Physics (02540584) 328
This study explores the structural, electronic, and magnetic characteristics of full-Heusler Ti2FexMn1-xAl alloys for spintronic applications. The regular Heusler structure is identified as the most stable across all x concentrations. The inverse Heusler structure exhibits half-metallic behavior with a finite energy band gap in the spin-up states, while the regular structure shows metallic behavior for both spin directions. Dirac-like points along the M→Γ direction are observed, particularly in alloys with x = 0 and 0.25 (inverse structure) and x = 0.5, 0.75, and 1 (regular structure), indicating advanced electronic properties. Magnetic analysis reveals that Ti atoms' local magnetic moments are antiparallel to those of Mn and Fe atoms. The total magnetic moment is highest for x = 1 (Ti2MnAl) and nearly zero for x = 0 (Ti2FeAl). Additionally, the inverse Heusler structure achieves 100 % spin polarization at the Fermi energy, underscoring its suitability for spintronic applications. This study highlights the potential of Ti2FexMn1-xAl alloys for future spintronic devices. © 2024 Elsevier B.V.
Materials Today Electronics (27729494) 9
This study conducts a comprehensive first-principles analysis of the structural, mechanical, phonon dispersion, and electronic properties of XMg2Hg, XMgHg2, and X2MgHg (X = Sc and Li) compounds. Using energy-volume curves, cohesive and formation energy, and phonon dispersion analyses, we confirm the stability of these compounds. Our calculations reveal that Li2MgHg and ScMg2Hg are more stable in the cubic structure with space group F4¯3m (216), whereas other compounds are stable in the Fm3¯m (225) structure. Phonon dispersion calculations indicate dynamical stability for all compounds except Li2MgHg in the Fm3¯m structure and Sc2MgHg and LiMg2Hg in the cubic structure with space group F4¯3m (216). Mechanical stability is confirmed through the calculation of elastic constants, with Sc-based compounds showing higher bulk modulus, shear modulus, and Young's modulus compared to Li-based compounds. Electronic properties, analyzed through density of states and band structure calculations, confirm the metallic nature of these compounds, with significant contributions from Mg atoms at the Fermi energy. The study also identifies distinct electronic features such as flat electron bands and a Dirac point at the Gamma point for ScMgHg2. Pressure-dependent studies indicate these materials are normal metals without topological phase transitions. © 2024 The Author(s)
Journal of Magnetism and Magnetic Materials (03048853) 588
We investigate energy spectra of Bi honeycomb quantum dots (BiQDs) considering buckled hexagonal and triangular structures with zigzag and armchair edges. We apply the four-orbital tight-binding approach. By using of the probability density of states, we distinguish some edge states in the regime of the band gap of Bi monolayer. We see that the number of edge states of zigzag (armchair) triangular BiQDs is more than the number of edge states of zigzag (armchair) hexagonal BiQDs. Also, we investigated energy spectra of hexagonal and triangular BiQDs with zigzag and armchair edges in the presence of the perpendicular magnetic fields. In the low and strong magnetic fields, there are relativistic Landau levels in the electronic spectra of BiQDs (in the hexagonal and triangular boundary conditions). Moreover, we show that edge atoms have more important roles in the formation of the line connectors between i and |i+1| Landau levels of hexagonal BiQDs than ones that are in the triangular BiQDs. In the middle numbers of the magnetic fields, more states collapse into Landau levels in which bulk atoms have a significant role to constitute them in both hexagonal and triangular BiQDs. Furthermore as the same as Bi nanoribbon spectrum, there are some helical edge modes in the band gap regions of Bi monolayer in which edge atoms are responsible to form them. These helical edge modes have topological properties. © 2023 Elsevier B.V.
COMPUTER PHYSICS COMMUNICATIONS (00104655) 288
We fixed Fig. 1 in the paper [1] by correcting, and <. We also removed the first row in the figure where E and G were zero, because having those values can make the crystal unstable. We made some changes to the equations in the paper. In subsection 2.1, we modified Eq. 2 to look like this: [Formula Presented] In subsection 2.2, we improved Eq. 8 to remove ambiguity: Furthermore, we changed the range of angle φ in Eq. 12 from 0 2π. Subsection 2.1 of the paper now includes modifications to the number of independent elastic constants for various crystal classes: 21 for triclinic, 13 for monoclinic, 9 for orthorhombic, 6 or 7 for rhombohedral (depending on the Laue class [2]), 6 or 7 for tetragonal (depending on the Laue class [2]), 5 for hexagonal, and 3 for cubic. In subsection 3.1, four methods for the Born elastic stability conditions for a crystal are listed. These methods are valid for all crystal symmetries [2]: 1) if the second-order elastic stiffness tensor Cij is positive definite, 2) if all eigenvalues of are all positive. We have added reference [2] for these conditions. Additionally, we modified the term “definitely positive” in condition (1) to “positive definite” for mathematical accuracy. We have corrected the term “NCL” to “NLC” in subsection 3.4. The corrected sentence reads: “The NLC of ZnAu2(CN)4 was predicted in Ref. [61], which is evident in the z-direction.” © 2023 Elsevier B.V.
Physical Chemistry Chemical Physics (14639084) 25(17)pp. 12182-12191
Two-dimensional (2D) topological insulators (TIs) hold great promise for future quantum information technologies. Among the 2D-TIs, the TiNI monolayer has recently been proposed as an ideal material for achieving the quantum spin Hall effect at room temperature. Theoretical predictions suggest a sizable bandgap due to the spin-orbit coupling (SOC) of the electrons at and near the Fermi level with a nontrivial 011111111100 011000010100 000000100100 000001001000 000010001000 000010110000 000100100000 000101000000 001001000010 010010000110 011111111110 2 topology of the electronic states, which is robust under external strain. However, our detailed first-principles calculations reveal that, in contrast to these predictions, the TiNI monolayer has a trivial bandgap in the equilibrium state with no band inversion, despite SOC opening the bandgap. Moreover, we show that electron correlation effects significantly impact the topological and structural stabilities of the system under external strains. We employed a range of density functional theory (DFT) approaches, including HSE06, PBE0, TB-mBJ, and GGA+U, to comprehensively investigate the nontrivial topological properties of this monolayer. Our results demonstrate that using general-purpose functionals such as PBE-GGA for studying TIs can lead to false predictions, potentially misleading experimentalists in their efforts to discover new TIs. © 2023 The Royal Society of Chemistry.
Physica B: Condensed Matter (09214526) 659
Using the multi-orbital (sp3) tight-binding (TB) model, we have obtained the band structure of the Antimony monolayer with a hexagonal array of holes. These structures are named Antimony antidot lattice (AAL). In our tight-binding model, the interaction of the nearest and next-nearest neighbors of atoms has been considered. Our numerical results present that band structures of the system depend on the size of embedded holes in the Antimony monolayer as points of the antidot lattice. Also, we have shown that AALs with a large radius of holes are almost conductors with tiny energy gaps. Besides, we have represented that spin–orbit coupling magnificently affects the band gap for Antimony antidot lattice in the different ranges of hole radius. Moreover, we have investigated the effect of distance between holes of AALs on the band structure and energy gap. Also, the variations of the band gap of Antimony antidot by changing the inserted strain on it have been investigated. Furthermore taking into account the effect of strain, we have compared the band structure and energy gap of antidot lattice (Highlightslayer with hole) and ideal sheet (monolayer without hole). Finally, the effect of substrate on the electronical properties of Antimony monolayer with holes (Antidot) and without holes (ideal sheet) is analyzed. © 2023
Journal of Materials Science (15734803) 58(24)pp. 10023-10042
This study conducts a thorough examination of the properties of four transition-metal dichalcogenides (TMDCs): WTe2, WSe2, ZrTe2, and NiTe2, using first-principles density functional theory calculations. The results reveal that WSe2 and WTe2 exhibit semiconducting behavior in both bulk and monolayer forms, while ZrTe2 and NiTe2 exhibit metallic behavior in their bulk forms. However, a deviation from metallic behavior is observed in the monolayer form of NiTe2. The study also delves into the optical characteristics of both bulk and monolayer forms, including dielectric function, reflectivity, absorption coefficient, refraction coefficient, and electron energy loss function. These findings provide a comprehensive understanding of the properties of these TMDCs, which can be utilized in the design of advanced optoelectronic devices. Moreover, the observed decrease in absorption coefficient in the monolayer forms of these TMDCs can be leveraged for transparent conductor technology. Overall, this study presents a detailed analysis of the properties of TMDCs, highlighting their potential for technological exploitation in a wide range of optoelectronic applications. © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
Journal of Materials Science (15734803) 58(24)pp. 10217-10217
The original online version of this article was revised to correct typesetting errors. © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
Computer Physics Communications (00104655) 271
We introduce a computational method and a user-friendly code with a terminal-based 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 integrated to conveniently interface with GNUPLOT, XMGRACE, view3dscene and plotly libraries, offering immediate post-processing of the results. ElATools provides reliable means to investigate the mechanical stability based on the calculation of six (three) eigenvalues of the elastic tensor in 3D (2D) materials. It can efficiently identify anomalous mechanical properties, such as negative linear compressibility, negative Poisson's ratio, and highly-anisotropic elastic modulus in 2D and 3D materials, which are central properties to design and develop high-performance nanoscale electromechanical devices. Moreover, ElATools can predict the behavior of the sound velocities and their anisotropic properties, such as acoustic phase/group velocities and power flow angles in materials, by solving the Christoffel equation. Six case studies on selected material systems, namely, ZnAu2(CN)4, CrB2, δ-phosphorene, Pd2O6Se2 monolayer, and GaAs, and a hypothetical set of systems with cubic symmetry are presented to demonstrate the descriptive and predictive capabilities of ElATools. Program summary: Title: ElATools Licensing provisions: GNU General Public Licence 3.0 Nature of the problem: Identifying anisotropic elastic properties of 2D and 3D materials, and calculating acoustic phase and group velocities in homogeneous solids. Solution method: Second-order elastic stiffness tensor analysis using transformation law and calculations of the elastic surfaces properties. Solving the Christoffel equation eigenvalue problem using diagonalization and calculations of the sound velocities. Programming language: Fortran 90 Operating system: Unix/Linux/MacOS/Windows by Cygwin: http://www.cygwin.com/ Distribution format: tar.gz Required routines/libraries: LAPACK, BLAS, and Plotly Javascript libraries, GNUPLOT, XMGRACE, view3dscene. Computer: Any system with a Fortran 90 (F90) compiler Memory: Up to 1 GB for any symmetry Run time: Up to 70 seconds for any symmetry, and (400×400) = (θ×ϕ)-mesh in spherical coordinate Documentation: Available at https://yalameha.gitlab.io/elastictools/index.html © 2021 Elsevier B.V.
Materials Science and Engineering: B (09215107) 281
(Si, Ge, Sn)-based alloys are generally compatible with silicon technology and offer many options to engineer the optical properties. Furthermore, topological phases in some of these alloys have been investigated. In this work, through the calculations of the first-principles, the possibility of realization of topological phases in new SnSi1-xGex alloys (x = 0.0, 0.25, 0.5, 0.75, and 1.0) by hydrostatic pressure has been investigated. Furthermore, the effects of Ge concentration and the hydrostatic pressure on the topological phase of these alloys are studied and the band inversion strength (BIS) as a function of concentration (x) and pressure is plotted in a matrix image. The calculations of electronic band structure and band inversion of these alloys within two generalized gradient approximation (GGA) and Heyd-Scuseria-Ernzerhof screened hybrid (HSE06) functional are compared. It was found that the HSE06 approach was more effective than the GGA approach in improving bandgap and BIS. The results show that the nontrivial topological phase of these alloys in both approaches is due to an s-p band inversion at the Gamma (G) point. Moreover, the calculated topological surface states and ℤ2-index confirm the topological phase transition in these alloys. According to the HSE06 approach, at x ≤ 0.5, pressure changes play an essential role in the topological phase transition, while at x > 0.5, pressure changes affect only the BIS. The SnSi1-xGex alloys are dynamically stable, and it is expected that these alloys can be experimentally synthesized. © 2022 Elsevier B.V.
Journal of Physics and Chemistry of Solids (00223697) 154
The quaternary alloys BeSiP2xAs2(1−x) with the noncentrosymmetric chalcopyrite structure are studied by means of ab initio density functional theory calculations. The calculations are shown the substitution of Asby P leads to the decrease of the volume of the unit cell and the increase of the energy band gap. Using the Zunger approach, the microscopic origins of the energy band gap bowing are examined in term of volume deformation bVD, charge exchange bCEand structural relaxation bS.The analysis of the total electron density distribution map is shown that the electrons flow from the As, Si and P atoms and accumulate into covalent bonds between the As and Si atoms and between the Si and P atoms. The effect of Pconcentration on the mechanical properties, phonon frequencies and Born effective charges Z∗ of these quaternary alloys are also investigated. The calculated results indicated that these quaternary alloys are mechanical and dynamically stable, have a brittleness character and can be regarded as elastically anisotropic materials. Moreover, the thermodynamic properties of these quaternary alloys including the heat capacity at constant volume CV, the Helmholtz free energy F and entropy S are calculated using the harmonic approximation based on the phonon density of states calculation. Finally, the nonlinear optical coefficient d36 of the quaternary alloys BeSiP2xAs2(1−x) is evaluated and the results confirm that these alloys are remarkable in the nonlinear optics. © 2021 Elsevier Ltd
Materials Science and Engineering: B (09215107) 273
We predict the highly stable new full-Heusler order compound Cs(Na, K)2Bi, that can take a diverse set of topological states by strain-engineering. Based on first-principles studies, our findings reveal that the hydrostatic lattice compression, uniaxial compression, and uniaxial tension can transition Cs(Na, K)2Bi to a trivial semiconductor, a normal insulator, a topological insulator, a Weyl semimetal, a Dirac semimetal, and a Nodal Line semimetal. These topological states, induced by various kinds of strain, exhibit a range of interesting optical and electronic transport properties. These results introduce Cs(Na, K)2Bi compounds as promising candidates to make novel topological devices whose properties can be controlled using strain-engineering. © 2021 Elsevier B.V.
Nanomaterials (20794991) 11(10)
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 CsNa2Bi, and Poisson’s ratio shows completely isotropic behavior under hydrostatic compression. A directional elastic wave velocity analysis shows that hydrostatic pressure effectively changes the propagation pattern of the elastic waves of both compounds and switches the directions of propagation. Cohesive energy, phonon dispersion, and Born–Huang conditions show that these compounds are thermodynamically, mechanically, and dynamically stable, confirming the practical feasibility of their synthesis. The identified mechanisms for controlling the auxetic and anisotropic elastic behavior of these compounds offer a vital feature for designing and developing high‐performance nanoscale electromechanical devices. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
Physica E: Low-Dimensional Systems and Nanostructures (13869477) 134
Strain engineering is a useful approach for tuning and advancing the physical features and characteristics of two-dimensional materials, because of their large susceptibility. Also, these materials are appropriate for the nanophotonic and nanoelectronic applications. So in this work, the equilibrium lattice parameter and phonon spectra of TiS monolayer are first calculated and investigated and the dynamic stability of this monolayer is proved at different uniaxial strains. Then the strain dependence of electronic and thermoelectric properties of TiS monolayer is studied by using generalized gradient approximation plus spin-orbit interaction. Furthermore, the effect of different uniaxial strains on the TiS monolayer optical constants is investigated. The noticeable transparency and reflectivity of this monolayer are observed at low energies. © 2021 Elsevier B.V.
Journal of Computational Electronics (15698025) 20(6)pp. 2300-2307
First-principles electronic, thermoelectric, thermodynamic, and optical calculations of an alkali pnictide compound, Li3Bi, 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 Li3Bi 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 Li3Bi at a pressure of 6 GPa. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
Journal of Physics Condensed Matter (09538984) 34(10)
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 andZ2topological 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 band dispersions show that these structures are mechanically and dynamically stable. Therefore, they offer excellent candidates for practical applications over a wide range of temperatures. © 2021 IOP Publishing Ltd.
Polash, M.M.H. ,
Yalameha, S. ,
Zhou, H. ,
Ahadi, K. ,
Norbakhsh, Z. ,
Vashaee, D. Materials Science and Engineering R: Reports (0927796X) 145
The spin-orbit coupling field, an atomic magnetic field inside a Kramers’ system, or discrete symmetries can create a topological torus in the Brillouin Zone and provide protected edge or surface states, which can contain relativistic fermions, namely, Dirac and Weyl Fermions. The topology-protected helical edge or surface states and the bulk electronic energy band define different quantum or topological phases of matters, offering an excellent prospect for some unique device applications. Device applications of the quantum materials rely primarily on understanding the topological properties, their mutual conversion processes under different external stimuli, and the physical system for achieving the phase conversion. There have been tremendous efforts in finding new topological materials with exotic topological phases. However, the application of the topological properties in devices is still limited due to the slow progress in developing the physical structures for controlling the topological phase conversions. Such control systems often require extreme tuning conditions or the fabrication of complex multi-layered topological structures. This review article highlights the details of the topological phases, their conversion processes, along with their potential physical systems, and the prospective application fields. A general overview of the critical factors for topological phases and the materials properties are further discussed to provide the necessary background for the following sections. © 2021
Physica E: Low-Dimensional Systems and Nanostructures (13869477) 127
In this work, some physical properties of ScX (X = Sb and Bi) nano-layers are evaluated based on DFT employing Wien2k code within generalized gradient approximation in presence of spin orbit coupling. The band order and topological phase of ScX (X = Sb, Bi) bulks are investigated and then the topological nature of these bulks is examined by the investigation of surface states topological phase of ScX nano-layers with different thicknesses. The bonding type between the surface atoms of ScX nano-layers is also investigated. Furthermore, the optical properties of ScX nano-layers are investigated and compared. The results show the high contribution of intraband transitions and consequently high reflectivity and negative real part of dielectric function of these nano-layers near zero energy. The different responses of ScX nano-layers to the radiated electromagnetic waves in polarizations of parallel and perpendicular to their surfaces imply the anisotropic optical features of these nano-layers in x (or y) and z directions. © 2020 Elsevier B.V.
Journal of Physics Condensed Matter (09538984) 32(29)
In recent years, topological semimetals such as Weyl, Dirac, and nodal-line semimetals have been a hot topic in thefield of condensed matter physics. Depending on the orientation of band crossing in momentum space, topological semimetals and metals can be identi_ed as type-I or type-II. Here, we report the coexistence of two new types of topological metal phase in the ScM (M = Cu, Ag, Au) intermetallic compounds (IMCs): (1) multi-nodal-lines semimetals (above Fermi energy), (2) critical-type nodal-lines (lower than Fermi energy). The_rst case has already been investigated. So, in this paper, we focus on the second case. We_nd that these IMCs can be an existing topological metal lower than Fermi energy, which are characterized with type-I (for ScCu and ScAu) and critical-type (for ScAg) nodal-lines in the bulk and drumhead liked surface states in the absence of the spin-orbit coupling (SOC). It has also been shown that when SOC is included, these compounds are converted into topological metal materials. © 2020 Institute of Physics Publishing. All rights reserved.
Journal of Magnetism and Magnetic Materials (03048853) 503
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 energy loss function of these NLs in some specific energy ranges. © 2020 Elsevier B.V.
Journal of Physics and Chemistry of Solids (00223697) 143
The structural, electronic, optical and elastic properties of CsCdxPb1−xCl3alloys are studied using the plane-wave pseudopotential method under the framework of density functional theory (DFT). The Perdew–Burke–Ernzerhof functional (GGA−PBE)is employed to treat the exchange and correlation potentials. The supercell approach (SC)and the virtual crystal approximation (VCA)are also used to model the CsCdxPb1−xCl3alloys. Because of the symmetry constraint in the VCAapproach, the calculated lattice parameters of these alloys only within SCapproach show linear behavior in agreement with the Vegard's law. Using the approach of Zunger and co-workers, the microscopic origin of the energy band gap bowing of these alloys is investigated in terms of the volume deformation, charge exchange and structural relaxation. The energy band gap of these alloys is also predicted to be suitable for solar absorber applications. The real and imaginary parts of the macroscopic dielectric function (MDF)of CsCdxPb1−xCl3alloys are studied using the single-particle picture within random phase approximation (RPA). The calculated static dielectric constant of these alloys increases when Cdconcentration decreases. To study the excitonic effects (EXC), the macroscopic dielectric function of these alloys is also calculated through the solution of the Bethe-Salpeter equation (BSE)using Tamm-Dancoff approximation within many-body perturbation theory. The variation of some polycrystalline structural properties of these alloys such as the Bulk modulus, Young's modulus, Poisson's ratio, Pugh's ratio, shear and Zener's anisotropy parameters as a function of the Cdconcentration are studied using perturbation density functional theory (PDFT). The calculated results show that these alloys are mechanically stable and rather elastically anisotropic. This study provides a detailed theoretical analysis of the CsCdxPb1−xCl3alloys and can give helpful guidance for further relevant research. © 2020
Journal of Physics Condensed Matter (09538984) 32(25)
Topological insulators with novel surfaces or edge states are the topological nature sequel of bulk electronic wave functions of these materials. The observed signatures in the electronic structure of topological insulators can make them excellent candidates for thermoelectric materials. Low dimensional materials such as phosphorene and Bi2Te3 nanowire have been confirmed to be desirable for the design of devices with high thermoelectric performance. So in this work, the phonon modes, formation energy and cohesive energy of LaX (X = Sb, Bi) monolayers are first calculated and investigated. Then the band order of these monolayers is investigated by the band structure calculations and the topological phase of these monolayers is proved by using the calculation of Z 2 topological invariant. The energy band gap and the band inversion strength of these monolayers are evaluated under in-plane strains. Also, the effect of different temperatures and in-plane strains on the thermoelectric performance of LaX monolayers is studied. The results show the high thermoelectric efficiency and d-p topological band inversion of these monolayers under compressive strains. © 2020 IOP Publishing Ltd.
Journal of Applied Physics (10897550) 127(8)
Topological materials are considered as a novel quantum state of matter, which can be characterized by symmetry-protected Dirac interfacial states, and exhibit an exotic phenomenon when combined with the other phases. The topological phase in the perovskite structures is important since it can provide various heterostructure interfaces with multifunctional properties. Alpha-(α-) phase cesium-based halide perovskites CsSnX3 (X = I, Br, Cl) can be considered as a promising candidate for topological semiconductors under hydrostatic pressures. The narrow bandgap of these compounds (≤1.83 eV) has made them interesting materials for the electronic, optoelectronic, and photovoltaic applications. In the current research, we systematically carry out first-principles density functional theory (DFT) to study the effects of hydrostatic pressure on the electronic structure of CsSnX3 (X = I, Br, Cl) compounds. The topological phase of these compositions is investigated using the Fu-Kane and Wilson loop methods in order to identify the Z2 topological invariants for each structure. The topological surface states (TSSs) of the (001) plane of these compounds are investigated using the semi-infinite Green's function. These TSSs guarantee the nontrivial nature of CsSnX3 compounds under pressure. With respect to the engineering applications, three important mechanical properties of these compounds including elastic anisotropy, ductility, and hardness are also investigated. © 2020 Author(s).
Physica E: Low-Dimensional Systems and Nanostructures (13869477) 122
The investigations of quantum spin Hall effect and the edge states manipulation of two dimensional topological insulators are very salient for the practical applications and fundamental sciences. The high thermoelectric efficiency of these materials has also been confirmed, recently. So, in this study the first-principles calculations are implemented based on density functional theory in the presence of spin orbit interaction, to evaluate the topological phase transition and thermoelectric performance of XBi (X = Sc, Y) monolayers under in-plane strains. It is found that the compressive in-plane strains and spin orbit interaction, which host considerable effects on the electronic structure, can cause the topologically nontrivial phase and high thermoelectric performance. The topological state of XBi monolayers is confirmed with the Z2 topological invariant calculation. These results provide these monolayers for the novel thermoelectric and nanoelectronics quantum devices and topological phenomena. Also some optical properties of XBi monolayers are calculated and investigated under in-plane strains. The results show the considerable transparency and reflectivity of these monolayers near zero energy. © 2020 Elsevier B.V.
Journal of Physics and Chemistry of Solids (00223697) 145
In this study, we investigated some physical properties of AB (A = Sc, Y and B = Sb, Bi) compounds in different structural phases based on density functional theory. The effects of different hydrostatic pressures and biaxial strains on the band orders of AB compounds were investigated. The calculations were conducted with the Wien2k package in the presence of spin orbit coupling. The results showed that the topological d-p band inversion can be induced by appropriate compressive strains and spin orbit coupling. The topological phase of AB compounds was confirmed based on calculations of the Z2 topological invariant. The band inversions and strong topological phases of these compounds may make them suitable for appropriate applications in quantum computation and spintronics. Furthermore, we investigated and compared the optical properties of AB compounds, and the results indicated the high contributions of intraband transitions, high reflection, and negative real part of the dielectric function for these compounds near zero energy. © 2020 Elsevier Ltd
Solar Energy (0038092X) 184pp. 372-377
On the basis of density functional calculations and using Bader's atom in molecule theory, this article presents quantitative microscopic analyses on the bonding properties of amorphous silicon (a-Si) which could reflect in the observable mechanical and electronic behaviors of this material. In addition, the occurrence and strength of quantum confinement of charge carriers in a composition of silicon crystal nano slabs (SiNSs) embedded in hydrogenated a-Si (a-Si:H) semiconductor are studied. It is shown that the strongest confinement effect happens for Si slabs limited in [1 0 0] direction. The band gap tunability with the width of SiNSs is exhibited and a scaling law is investigated for the size dependent behavior of energy states. It is demonstrated and argued why in these systems the confinement of holes is stronger than electron confinement. The computational methodology used to passivate a-Si defects by hydrogen is also detailed. © 2019
Journal of Physics and Chemistry of Solids (00223697) 132pp. 213-221
The structural and electronic properties of InAsxSb1-x ternary alloys are studied using plane-wave pseudopotential method based on the density functional theory. The Born effective charge, elastic constants, phonon dispersion curves, linear and nonlinear optical properties of these compounds are calculated using density functional perturbation theory. Based on the calculated phonon frequency, the specific heat at constant volume and entropy are obtained within the harmonic approximation. Moreover, due to the density functional theory band gap problem, the band gap correction is performed within the one-shot GW approximations. The distinguished role of In 4d states on the electronic energy band gap and nonlinear properties of these alloys are extensively explored by the comparison between the calculated results of Hartwigsen-Goedecker-Hutter and Trouiller-Martins-type pseudopotentials. The calculated results show that InAsxSb1-x alloys are mechanically stable and can be a good candidate for high-performance nonlinear optical material. The calculated results of InAs and InSb compounds are in acceptable agreement with available theoretical and experimental results, so the calculated results of InAsxSb1-x alloys will be helpful for future experimental and theoretical investigations. © 2019 Elsevier Ltd
Computational Condensed Matter (23522143) 19
The first principle investigations of the structural, electronic, linear and nonlinear response properties of the zinc-blende ZnSe and ZnTe are performed based on the density functional theory using a plane-wave pseudopotential approach. The Born effective charges, piezoelectric tensor, phonon frequencies, LO–TO splitting and thermal properties of these compounds are calculated using a linear response method within the density functional theory framework. The macroscopic dielectric function is calculated in the response of the many body effects within the Bethe-Salpeter approach using the Tam-Dancoff approximation. The nonlinear response properties to atomic displacements and electric fields are investigated within the density functional perturbation theory framework based on the 2n+1 theorem as implemented by the ABINIT software. After the calculation of the Kohn–Sham electronic band structures, the correction of the energy band gap is computed using the GW approximation within the many-body perturbation theory framework (MBPT). The results are in excellent agreement with the available experimental and other theoretical results. © 2019 Elsevier B.V.
Indian Journal of Physics (09731458) 93(5)pp. 571-582
Our previous study of XFeSi (X = La, Gd, Tb) bulks shows that Fe atom has negligible contribution to the magnetic properties of these compounds. In this paper, the contribution of Fe atom to the magnetic properties of XFeSi (X = La, Gd, Tb) nano-layers is investigated. The calculated results are performed based on the density functional theory. The exchange–correlation potential is calculated using generalized gradient approximation and generalized gradient approximation plus Hubbard parameter. The structural, electronic and magnetic properties of XFeSi (X = La, Gd, Tb) nano-layers are investigated in the presence of spin–orbit coupling. The calculated results are compared with the corresponding results of their bulks. Furthermore, the thermodynamic properties of these nano-layers are investigated using the quasi-harmonic Debye model. The bulk modulus, Debye temperature, specific heat at constant pressure and volume and thermal expansion coefficient of these nano-layers are calculated and compared with the corresponding results of their bulks. © 2018, Indian Association for the Cultivation of Science.
Journal of Electronic Materials (03615235) 48(12)pp. 7977-7990
The Born effective charge tensors, high-frequency dielectric constants, phonon frequencies at Г symmetry point, and phonon dispersion curves of MoS2xSe2(1−x) (x = 0, 0.25, 0.5, 0.75, and 1) alloys are calculated based on density functional perturbation theory using optimized lattice parameters. The structural stability, stiffness, ductility, and plasticity of these alloys are explored in detail by calculating the polycrystalline structural properties. The calculated Born effective charges and Poisson’s ratio indicate the existence of a combination of ionic and covalent bonding between the transition metal and chalcogens in each layer. Based on the calculated phonon frequencies, the temperature dependence of the specific heat at constant volume, entropy, and Helmholtz free energy of MoS2xSe2(1−x) (x = 0, 0.25, 0.5, 0.75, and 1) alloys are calculated in the harmonic approximation. Structurally, the spatial inversion symmetry in the MoS2xSe2(1−x) (x = 0.25, 0.5, and 0.75) alloys is broken. This leads MoS2xSe2(1−x) (x = 0.25, 0.5, and 0.75) alloys to exhibit novel nonlinear optical properties that do not exist in the 2H-MoX2 (X = S, Se) compounds. So, the nonlinear optical properties are calculated by applying the 2n + 1 theorem to an electric-field-dependent energy functional. It is found that MoS2xSe2(1−x) (x = 0.25, 0.5, and 0.75) alloys exhibit remarkable large nonlinear optical susceptibility and electro-optic coefficients and would be promising candidates for use in nonlinear optical applications. Van der Waals interactions are included in all the first-principles calculations, to correctly describe the interaction between adjacent layers. The calculated lattice parameters, electronic energy bandgaps, phonon frequencies, and high-frequency dielectric constants of 2H-MoX2 (X = S, Se) compounds are in good agreement with available theoretical and experimental results. © 2019, The Minerals, Metals & Materials Society.
Computational Condensed Matter (23522143) 21
The structural, electronic, thermodynamic, vibrational, elastic, linear and nonlinear optical properties of AlxGa1-xP ternary alloys are studied using plane-wave pseudopotential method based on the density functional theory. The alchemical mixing method is used to construct an alloy by mixing the pseudopotentials in an appropriate way. The local density approximation is used for the exchange and correlation potentials calculations using the ABINIT code. The Born effective charges, phonon frequencies, longitudinal-transvers optical splitting and thermal properties are calculated using density functional perturbation theory. By applying the many-body effects within the Bethe-Salpeter approach using the Tam-Dancoff approximation, the frequency-dependent macroscopic dielectric function is calculated. The nonlinear dielectric (electronic) susceptibility, the electro-optic tensor and the Raman tensor are investigated in the framework of density functional perturbation theory using the 2n+1 theorem. Moreover, due to density functional theory band gap problem, the band-gap correction is performed within the one-shot GW approximation of many-body perturbation theory. The calculated results of AlP and GaP compounds are in acceptable agreement with available theoretical and experimental results, so the present study on the AlxGa1-xP alloys would be helpful for future experimental and theoretical investigations. © 2019 Elsevier B.V.
Physics Letters, Section A: General, Atomic and Solid State Physics (03759601) 383(2-3)pp. 221-230
First principle calculations have been employed to investigate the effects of Y concentration, pressure and temperature on various properties of Gd1−xYxAuPb (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 Gd1−xYxAuPb 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 Gd1−xYxAuPb alloys is proved using elastic constants calculations. Also, the influence of Y concentration on elastic properties of Gd1−xYxAuPb 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. © 2018 Elsevier B.V.
Indian Journal of Physics (09731458) 93(11)pp. 1427-1436
The WIEN2K package based on the density functional theory within the generalized gradient approximation (GGA) and GGA plus Hubbard parameter was applied to explore the structural, electronic, magnetic properties and topological phase of CeNiSb bulk and nano-layer (NL), in the presence of spin orbit coupling. Also the topological phase, band order and the linear coefficient of electronic specific heat of CeNiSb bulk and nano-layer are studied. The electronic charge distribution at this nano-layer surface, within GGA and GGA + U approaches, is calculated. © 2019, Indian Association for the Cultivation of Science.
Physical Review B (24699950) 97(23)
The effects of lattice distortion and chemical disorder on charge transport properties of two-terminal zigzag phosphorene nanoribbons (zPNRs), which shows resonant tunneling behavior under an electrical applied bias, are studied. Our comprehensive study is based on ab initio quantum transport calculations on the basis of the Landauer theory. We use nitrogen and silicon substitutional dopant atoms, and employ different physical quantities such as the I-V curve, voltage drop behavior, transmission spectrum, transmission pathway, and atomic current to explore the transport mechanism of zPNR devices under a bias voltage. The calculated transmission pathways show the transition from a ballistic transport regime to a diffusive and in some particular cases to localized transport regimes. Current flowing via the chemical bonds and hopping are monitored; however, the conductance originates mainly from the charge traveling through the chemical bonds in the vicinity of the zigzag edges. Our results show that in the doped systems, the device conductance decreases and the negative differential resistance characteristic becomes weak or is eliminated. Besides, the conductance in a pure zPNR system is almost independent of the ribbon width. © 2018 American Physical Society.
European Physical Journal B (14346028) 91(7)
In this study, Kondo behavior, electronic structure and magnetic properties of CeRuPO-nano-layer are investigated using the first principles calculations. The calculations are performed by employing the full potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). These properties are calculated in the presence of spin-orbit interaction. The exchange-correlation interaction is calculated within generalized gradient approximation (GGA). In addition, the GGA+U approach (where U is the Hubbard correlation term) is also employed to improve treatment of the f-electrons. The calculated partial electron density of states demonstrates that the hybridization between Ce-4f and Ru-5d orbitals and consequently Kondo effect changes at the surface of the CeRuPO-nano-layer compared to the bulk. The results show that due to the weaker Kondo effect at the surface of CeRuPO-nano-layer, the magnetic moment of Ce atoms enhances and the effective mass of the conduction electron reduces. © 2018, EDP Sciences, SIF, Springer-Verlag GmbH Germany, part of Springer Nature.
Journal of Superconductivity and Novel Magnetism (15571947) 31(1)pp. 209-216
The structural, electronic, and magnetic properties of Nd1−xLaxFeSi (x = 0, 0.25, 0.50, 0.75, and 1) alloys are investigated based on the first-principle density functional theory by using the full-potential linear muffin-tin orbital (FP-LMTO) method. The exchange-correlation potential is treated with local density approximation (LDA). In addition, to treat localization of 4f-electrons properly, the LDA + U approach (where U is the Hubbard correlation term) is also employed. The calculated structural, electronic, and magnetic properties of these alloys within LDA and LDA + U approaches are compared. The calculated lattice constants of these alloys as a function of x within the LDA + U approach are in the best agreement with linear Vegard’s rule. Most importantly, we focus on the magnetic properties of these alloys and find that the magnetic interaction between Nd atoms is the Rudermen-Kittel-Kasuya-Yosida (RKKY) interaction type. Iron does not carry magnetic moment in these alloys and has just an induced small magnetic moment from Nd atoms. © 2017, Springer Science+Business Media New York.
Journal of Magnetism and Magnetic Materials (03048853) 468pp. 279-286
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. © 2018 Elsevier B.V.
Physical Review B (24699950) 98(12)
Based on density functional simulations combined with the Landauer transport theory, the mechanical strain impacts on the chemical bonds of phosphorene and their effects on the electronic properties are studied. Moreover, the effect of the tensile strain along the zigzag direction on the charge transport properties of a two-terminal phosphorene device is evaluated. Enhancement of the intraplanar interactions, in particular between the next-nearest neighbors in strained phosphorene, is found to be essential in the band-structure evolution. The charge transport analyzing shows that phosphorene has a strong piezoconductance sensitivity, which makes this material highly desirable for high-pressure nanoelectromechanical applications. The piezoconductance gauge factor increases by strain from 46 in 5% tension to 220 in 12% tension, which is comparable to state-of-the-art silicon strain sensors. The transmission pathways monitor the current flowing in terms of the chemical bonds and hopping, however, the transport mostly arises from the charge transferring through the chemical bonds. The strong anisotropy in the transport properties along zigzag and armchair directions is observed. © 2018 American Physical Society.
Abbas emami, S.A. ,
Amirabadizadeh, A. ,
Norbakhsh, Z. ,
Baizaee, S.M. ,
Alavi sadr, S.M. Journal of Superconductivity and Novel Magnetism (15571947) 31(1)pp. 127-134
In this work, the structural, electronic, magnetic, and optical properties of Mn2ZrGa full-Heusler alloy were investigated by using density functional theory (DFT) calculations. It is found that the spin-up states have a metallic character, but the spin-down bands have a pseudo-gap at the Fermi level. The total spin magnetic moment of Mn2ZrGa (per formula unit) is 3.00 µB at an equilibrium lattice parameter of 6.15 Å. The calculations show that Mn2ZrGa is a ferrimagnetic with 81% spin polarization at equilibrium lattice parameter. The effect of lattice parameter distortion on the magnetic properties and spin polarization is also studied. It is found that the total magnetic moment preserves its value for a lattice parameter range of 5.96–6.30 Å. The decreasing of the lattice parameter leads to improvement of spin polarization. The real and imaginary parts of dielectric function and hence the optical properties including energy absorption spectrum, reflectivity, and optical conductivity are also calculated. The value of plasma frequency for spin-up and down electrons is located at 1.78 and 0.74 eV, respectively. © 2017, Springer Science+Business Media New York.
Journal of Alloys and Compounds (09258388) 768pp. 433-440
In this paper, the topological phase of LuX (X = Sb, Bi) compounds under hydrostatic and biaxial pressures is investigated based on first principles of density functional theory by WIEN2k package. To find out the Z2 topological invariants of centrosymmetric compounds with the time reversal symmetry, the Bloch functions parity analysis can be used via electronic band structure calculations. So in this paper the Z2 topological invariants of the LuX (X = Sb, Bi) compounds with the time reversal and inversion symmetries are calculated using this approach. The results show that the d-p band inversion can be occurred in these compounds due to spin orbit interaction and appropriate pressure. These compounds have the strong electronic interaction due to their large d-electronic orbitals near the Fermi energy. The dynamic stability of these compounds is verified by phonon modes analysis. The surface states topological phase of these compounds are investigated based on the band structure calculations. © 2018 Elsevier B.V.
Journal of Magnetism and Magnetic Materials (03048853) 451pp. 681-687
Topological phase of Gd1−xYxAuPb (x = 0, 0.25, 0.5, 0.75, 1) alloys have been studied utilizing density function theory by WIEN2k code. The generalized gradient approximation (GGA), generalized gradient approximation plus Hubbard parameter (GGA + U), Modified Becke and Johnson (MBJ) and GGA Engel-vosko in the presence of spin orbit coupling have been used to investigate the topological band structure of Gd1−xYxAuPb alloys at zero pressure. The topological phase and band order of these alloys within GGA and GGA + U approaches under hydrostatic pressure are also investigated. We find that under hydrostatic pressure in some percentages of Gd1−xYxAuPb (x = 0, 0.25, 0.5, 0.75, 1) alloys in both GGA and GGA + U approaches, the trivial topological phase is converted into nontrivial topological phase. In addition, the band inversion strength versus lattice constant of these alloys is studied. Moreover, the schematic plan is represented in order to show the trivial and nontrivial topological phase of Gd1−xYxAuPb (x = 0, 0.25, 0.5, 0.75, 1) alloys in both GGA and GGA + U approaches. © 2017 Elsevier B.V.
Amirabadizadeh, A. ,
Emami, S.A.A. ,
Norbakhsh, Z. ,
Alavi sadr, S.M. ,
Baizaee, S.M. Journal of Superconductivity and Novel Magnetism (15571947) 31(5)pp. 1515-1525
The structural, electronic, magnetic, and optical properties of Mn-based Heusler Mn2ZrGa1−xGex (x = 0, 0.25, 0.5, 0.75, and 1) alloys are calculated by first-principles full-potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method. It is found that Mn2ZrGa1−xGex alloys are half-metallic ferrimagnetic and their magnetic moments are in good agreement with the Slater–Pauling relationship. The calculations reveal that all alloys have a pseudo-gap in the majority-spin channel except for x = 0.75 and x = 1 which have a real gap in the majority-spin channel. The spin polarization is quite large for whole series, and it reaches to a value of 100% for x = 0.75 and x = 1. Our calculated results clearly show that with the Ge substitution, the lattice parameter linearly decreases while the bulk modulus increases. Moreover, the calculated formation energies confirm that these alloys are stable chemically. The optical properties, including the real and imaginary parts of the dielectric function, reflectivity, and absorption spectra, were also investigated. The results show that the dominant behavior, at energy below 1 eV, is due to interactions of free electrons in the system. The increment of Ge concentration leads to an increase in the plasma frequency of metallic spin channel. © 2017, Springer Science+Business Media, LLC.
Journal of Superconductivity and Novel Magnetism (15571947) 30(8)pp. 2143-2158
The structural, electronic, magnetic, and thermodynamic properties of XFeSi (X = Gd, Tb, La) and GdRuSi compounds are investigated using density functional theory by the WIEN2k code. Using the first-principle procedure, the Hubbard parameter of Gd and Tb 4f electrons and La 5d electrons of XFeSi (X = Gd, Tb, La) and GdRuSi compounds is calculated. The structural and electronic and magnetic properties of these compounds within GGA and GGA + U approaches in the presence of spin-orbit coupling are calculated and compared. The calculated results indicate that the ferromagnetic phase is the most stable phase of XFeSi (X = Gd, Tb) and GdRuSi compounds and the nonmagnetic phase is the stable phase of LaFeSi. The magnetic moment of GdFeSi, GdRuSi, and TbFeSi compounds is due to Gd and Tb atoms. The calculated electronic band structures of these compounds show that these compounds have metallic behavior. Furthermore, the thermodynamic properties of these compounds using the quasi-harmonic Debye model as a function of temperature and pressure within GGA and GGA + U approaches are investigated. © 2017, Springer Science+Business Media New York.
Journal of Magnetism and Magnetic Materials (03048853) 426pp. 287-293
The structural, electronic and magnetic properties and Kondo behavior of Ce1−xLaxRuPO(x=0, 0.25, 0.5, 0.75 and 1) alloys are investigated using density functional theory by utilizing Wien2k package. The exchange-correlation potential is treated with the generalized gradient approximation (GGA). Moreover, the GGA+U approach (where U is the Hubbard correlation term) is employed to treat the f-electrons properly. We also present a comparative study between the electronic structure and magnetic properties of these alloys within GGA and GGA+U approaches. The calculated lattice parameters and bulk moduli of these alloys as a function of x are in the best agreement with Vegard's linear rule. The total and partial electron density of states and linear coefficient of electronic specific heat of these alloy within GGA and GGA+U are investigated and compared. The effect of La substitution on the Kondo behavior of CeRuPO compound is investigated. © 2016 Elsevier B.V.
Amirabadizadeh, A. ,
Emami, S.A.A. ,
Norbakhsh, Z. ,
Sadr, S.M.A. ,
Baizaee, S.M. Journal of Superconductivity and Novel Magnetism (15571947) 30(4)pp. 1035-1049
The structural, electronic, and magnetic properties and existence of the topological insulator and metal phase of full-Heusler Mn2ZrGa1−xAsx (x = 0, 0.25, 0.5, 0.75, 1) alloys are studied by using the first-principles full-potential linearized augmented plane wave (FP-LAPW) method. The electronic structure results indicate that the half-metallic character for the whole series exhibits a pseudo-gap for compounds with x = 0, 0.25, and 1 and a real gap for x = 0.5 and 0.75. It was found that the total magnetic moment decreases linearly with increasing As content and follows the Slater–Pauling rule. The results also predict that the whole series from x = 0 to 1 shows ferrimagnetic ordering with antiparallel alignment between Mn and Zr moments. The results of the topological band structure show that for the equilibrium lattice parameter, the Mn2ZrGa1−xAsx alloys have normal band order. Moreover, the effect of lattice parameter change on the band order of these alloys is investigated. By increasing the lattice parameter, the inverted band order occurs for the Mn2ZrAs compound. © Springer Science+Business Media New York 2016.
Amirabadizadeh, Ahmad ,
Amirabadizadeh, A. ,
Abbas emami, S.A. ,
Norbakhsh, Z. ,
Alavi sadr, S.M. ,
Baizaee, S.M. JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM (15571939) 30(4)pp. 1051-1051
The original version of this article unfortunately contained a mistake. The symbol As for Arsenic was incorrectly presented as “as”. The original article was corrected. © 2016, Springer Science+Business Media New York.
Thin Solid Films (00406090) 634pp. 112-120
The topological phase and optical properties of LuNiBi bulk and nano-layer are studied. The self-consistent calculations are carried out in presence of spin-orbit coupling, based on density functional theory using generalized gradient approximation, local density approximation, Engle-Vosco generalized gradient approximation and modified Becke and Johnson potential. The effect of hydrostatic and uniaxial pressures on band order, energy band gap and optical properties of LuNiBi compound is investigated within different approaches. The topological phase of surface states and the optical properties of LuNiBi nano-layer are studied. The results show that the topological phase and energy gap of LuNiBi bulk and nano-layer are sensitive to pressure and type of exchange-correlation potential. There is an anisotropic response of LuNiBi nano-layer to the incident electromagnetic waves polarizations, parallel and perpendicular to the nano-layer surface. © 2017 Elsevier B.V.
Journal of Magnetism and Magnetic Materials (03048853) 434pp. 62-67
The electronic, magnetic and optical properties of X-doped ScPdBi (X = Gd, Np, Cm) are investigated in the framework of density functional theory. The exchange-correlation potential is treated using generalized gradient approximation with Coulomb interaction parameter. The band order and energy band gap of X-doped ScPdBi are investigated by calculation of band structure. The effect of doping impurity on magnetic properties of ScPdBi compound is studied by calculation of total and partial magnetic moments of X-doped ScPdBi compound. Furthermore, the optical properties of X-doped ScPdBi are calculated and compared in the energy range of 0–25 eV. © 2017
Journal of Physics and Chemistry of Solids (00223697) 102pp. 121-129
The electronic, thermodynamic and optical properties of XPtSb (X=Lu, Sc) half Heusler compounds are studied based on density functional theory. The calculations are carried out in the presence of spin orbit interaction. The exchange correlation part of total energy is calculated within local density approximation, generalized gradient approximation, Engel-Vosco generalized gradient approximation and modified Becke and Johnson exchange potential with the correlation potential of the generalized gradient approximation. The effect of pressure on the electron density of states and linear coefficient of the electronic specific heat is studied. Using the band structure calculations at different pressures, the band inversion strength and topological phase transition of these compounds are investigated. Some thermodynamic properties of XPtSb compounds by different thermal models using the non-equilibrium Gibbs function are studied and compared with experiment. Furthermore the effect of pressure on dielectric function of XPtSb (X=Lu, Sc) compounds is investigated. © 2016 Elsevier Ltd
Thin Solid Films (00406090) 612pp. 214-224
The electronic and linear optical properties of pure graphene and impurity-graphene (with Fe, Co, Si and Ge impurities) sheets are investigated by using the full potential linear augmented plane wave plus local orbital (FPLAPW + lo) in the framework of the density functional theory (DFT). The calculated results are obtained within the generalized gradient approximation using the Perdew-Burke-Ernzerhof scheme in the presence of spin-orbit interaction. The band structure, partial electron density of states, dielectric function, absorption coefficient, optical conductivity, extinction index, energy loss function, reflectivity and the refraction index of these sheets for parallel and perpendicular electromagnetic wave polarization to sheet are investigated. The optical conductivity of Si-graphene and Ge-graphene sheets for the parallel electromagnetic wave polarization to the sheet starts with a gap about 0.4 eV confirms that these sheets have semiconductor behavior. Also the optical spectra of these sheets are anisotropic along these two wave polarizations. The dielectric function in the static limit of pure graphene sheet for perpendicular electromagnetic wave polarization to sheet does not significant change in the presence of Si, Ge, Fe and Co impurities. The static refractive index of Fe-graphene and Co-graphene sheets for parallel electromagnetic wave polarization to sheet is much larger than the corresponding value of pure graphene sheet. © 2016 Elsevier B.V. All rights reserved.
Chinese Physics B (16741056) 25(3)
The electronic properties and topological phases of ThXY (X = Pb, Au, Pt, Pd and Y = Sb, Bi, Sn) compounds in the presence of spin-orbit coupling, using density functional theory are investigated. The ThPtSn compound is stable in the ferromagnetic phase and the other ThXY compounds are stable in nonmagnetic phases. Band structures of these compounds in topological phases (insulator or metal) and normal phases within generalized gradient approximation (GGA) and Engel-Vosko generalized gradient approximation (GGA-EV) are compared. The ThPtSn, ThPtBi, ThPtSb, ThPdBi, and ThAuBi compounds have topological phases and the other ThXY compounds have normal phases. Band inversion strengths and topological phases of these compounds at different pressure are studied. It is seen that the band inversion strengths of these compounds are sensitive to pressure and for each compound a second-order polynomial fitted on the band inversion strengths-pressure curves. © 2016 Chinese Physical Society and IOP Publishing Ltd.
Thin Solid Films (00406090) 616pp. 287-296
The electronic and optical properties of XPdBi (X = Lu, Sc) nano-layers are investigated in the framework of first principles density functional theory by Wien2k code. The exchange-correlation potential is calculated within the generalized gradient approximation and Engel-Vosco generalized gradient approximation. The effect of nano-layer thickness on the electron density of states, energy gap and topological phase of these nano-layers is studied and compared. The surface states of LuPdBi nano-layers undergo a topological phase transition with increasing the thickness. The charge density of XPdBi nano-layers surface atoms with two different thicknesses is investigated. The results show the ionic bonding between X and Bi surface atoms of these nano-layers. The electric field gradient and the interaction of electronic orbital wave functions with the electronic cloud distribution of these nano-layers surface atoms with different thicknesses are calculated and compared. The anisotropic optical response of these nano-layers to two electromagnetic waves polarizations is investigated. Furthermore, the effect of nano-layer thickness on the optical properties of these nano-layers is studied in the 0–35 eV energy range. © 2016
Physical Review B (24699950) 94(3)
On the basis of many-body ab initio calculations, using the single-shot G0W0 method and Bethe-Salpeter equation, we study phosphorene nanoribbons (PNRs) in the two typical zigzag and armchair directions. The electronic structure, optical absorption, electron-hole (exciton) binding energy, exciton exchange splitting, and exciton wave functions are calculated for different sizes of PNRs. The typically strong splitting between singlet and triplet excitonic states make PNRs favorable systems for optoelectronic applications. Quantum confinement occurs in both kinds of PNRs, and it is stronger in the zPNRs, which behave like quasi-zero-dimensional systems. Scaling laws are investigated for the size-dependent behaviors of PNRs. The first bright excitonic state in PNRs is explored in detail. © 2016 American Physical Society.
Chinese Physics B (16741056) 25(9)
The thermal properties of pure graphene and graphene-impurity (impurity = Fe, Co, Si, and Ge) sheets have been investigated at various pressures (0-7 GPa) and temperatures (0-900 K). Some basic thermodynamic quantities such as bulk modulus, coefficient of volume thermal expansion, heat capacities at constant pressure and constant volume of these sheets as a function of temperature and pressure are discussed. Furthermore, the effect of the impurity density and tensile strain on the thermodynamic properties of these sheets are investigated. All of these calculations are performed based on the density functional theory and full quasi harmonic approximation. © 2016 Chinese Physical Society and IOP Publishing Ltd.
Tavakoli, M.M. ,
Tavakoli, R. ,
Norbakhsh, Z. ,
Waleed, A. ,
Virk, U.S. ,
Fan, Z. Advanced Materials Interfaces (21967350) 3(11)
Fabrication of organohalide perovskite materials on the top of ZnO nanoparticles (NPs) has some beneficial advantages such as room temperature processing; however, the perovskite is not stable on ZnO NPs layer during the annealing process. In fact, there are only a few reports about the fabrication of perovskite solar cells on ZnO NPs layer. Herein, the decomposition mechanism of CH3NH3PbI3 perovskite materials on ZnO is reported, and it is found that the perovskite film on the top of the ZnO layer is converted into PbI2 during the annealing process due to the existence of hydroxide groups on the surface of the ZnO NPs. Depending on the annealing temperature, the reaction rate and the quality of the perovskite film can be changed. In order to tackle this problem, a quasi core shell structure of ZnO/reduced graphene oxide (rGO) quantum dots is synthesized and is employed as an electron transfer layer. In this regard, rGO not only passivates the surface of the ZnO NPs to prevent the reaction, but also extracts the charge carriers quickly from the perovskite layer to reduce the carrier recombination. Our results show that perovskite solar cell on ZnO/rGO layer exhibits a stable power conversion efficiency as high as 15.2% and 11.2% on fluorine-doped tin oxide (FTO) glass and polyethylene terephthalate (PET) substrates, respectively, under AM1.5G illumination. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Journal of Superconductivity and Novel Magnetism (15571947) 29(4)pp. 985-993
The structural, electronic, and magnetic properties of pure graphene sheet and graphene sheet with Fe, Co, Si, and Ge impurities are investigated. The calculated results are done within density functional theory in the presence of spin-orbit coupling using the generalized gradient approximation. Electron density of states, band order, electron charge distribution, magnetic moment of these sheets, and the effect of pressure on the band order of graphene sheet with Fe impurity are investigated. © 2016, Springer Science+Business Media New York.
Modern Physics Letters B (02179849) 30(14)
In this paper, the structural, electronic and optical properties of LuPdBi and ScPdBi compounds are investigated using the density functional theory by WIEN2K package within the generalized gradient approximation, local density approximation, Engel-Vosco generalized gradient approximations and modified Becke-Johnson potential approaches. The topological phases and band orders of these compounds are studied. The effect of pressure on band inversion strength, electron density of states and the linear coefficient of the electronic specific heat of these compounds is investigated. Furthermore, the effect of pressure on real and imaginary parts of dielectric function, absorption and reflectivity coefficients of these compounds is studied. © 2016 World Scientific Publishing Company.
Journal of Magnetism and Magnetic Materials (03048853) 396pp. 106-112
The structural, electronic and magnetic properties and existence of topological phase of GdxY1-xPtBi (x=0, 0.25, 0.5, 0.75, 1) alloys are studied using density functional theory. The lattice constant and bulk modulus of these alloys in ferromagnetic phase are calculated using the generalized gradient approximation (GGA) in the presence of spin-orbit coupling. To investigate the electronic properties and existence of topological phase, the local density approximation (LDA), GGA and Engel-Vosko generalized gradient approximation (EV-GGA) are used. The electron density of states, band structure and topological band order of these alloys are investigated. Furthermore the variations of magnetic momentum, the linear coefficient of electronic specific heat and the band inversion strength with increase of x are investigated. © 2015 Elsevier B.V. All rights reserved.
Journal of Superconductivity and Novel Magnetism (15571947) 28(7)pp. 2133-2141
We have investigated the structural, electronic, and topological band structures and the linear coefficient γ of the electronic-specific heat and magnetic properties for ferromagnetic phase of CePdBi in bulk and nanolayers using density functional theory. The total energies as a function of volume are calculated and the bulk modulus and their pressure derivatives are determined. Also, the total energy calculation within generalized gradient approximation (GGA), local density approximation (LDA), and (LDA + U) indicate that at zero pressure the ferromagnetic phase of CePdBi compound is the most stable phase. This result is in agreement with the experimental results. The GGA and Engel–Vosko generalized gradient approximation have been used to obtain the band inversion strength and band order. The effect of hydrostatic pressure on the band inversion strength, band order, and total and local magnetic moments of CePdBi in bulk has been investigated. The magnetic moment decreases with the increasing pressure. The calculations of the structural, electronic properties, topological band structures, magnetic moment, and the linear coefficient γ of the electronic-specific heat have been performed under the presence of spin–orbit coupling. As far as we know, this is the first report on the pressure dependence of the magnetic moment of this compound and the electronic and magnetic properties and the linear coefficient γ of the electronic-specific heat of CePdBi nanolayers. © 2015, Springer Science+Business Media New York.
Journal of Superconductivity and Novel Magnetism (15571947) 28(3)pp. 943-947
In this paper, the magnetic and optical properties of ErP and ErSb nanolayers have been investigated in the presence of spin-orbit coupling using density functional theory by Wien2k package. The total energy of ErP and ErSb nanolayers as a function of unit cell volume is calculated in ferromagnetic and nonmagnetic phases using generalized gradient approximation (GGA) approach. It is seen that at zero pressure, the ferromagnetic phase is more stable than nonmagnetic phase. The density of states (DOS) calculation shows that the major contribution to the occupied part of DOS around the Fermi energy comes from 4f orbital of Er and p orbital of P and Sb atoms. The dielectric functions and other optical properties of these compounds have anisotropic behavior. The maximum reflectivity of these nanolayers occurs in the ultra-violet range; then, these nanolayers could be good candidates for shielding ultraviolet radiations. © 2014, Springer Science+Business Media New York.
Thin Solid Films (00406090) 556pp. 425-433
The optical properties of α-CuSe bulk and its nano-layers (NLs) have been studied by the first principles theoretical study in the framework of density functional theory. These properties are calculated with regard to dielectric function, refractive index, extinction coefficient, reflection coefficient, absorption coefficient, energy-loss function, and optical conductivity. To create NLs, two different thicknesses through CuSe bulk are chosen in the (0001) direction as the first and second thicknesses. The former thickness is divided into six different NLs with variant alternations. These NLs have the same chemical composition and are structural isomers. Among the NLs, the optical properties of the most stable NL and its double thickness are calculated and compared with the bulk state. The imaginary part of dielectric function has a main peak at low energies because α-CuSe is a conductive compound in the bulk state. The electronic structure of NLs shows that they have remained conductive in x (or y) direction, but they interestingly have a dielectric behavior with an ultra-low electrical conductivity in z direction. The optical curves in the bulk and NLs show the anisotropic feature between x and z directions. In the range of infrared to red light, the bulk refractive index, nz(ω), is very large, about 6, while n x(ω) is about 3. Results show that the NLs have wide absorption curves in the range of solar spectrum from infrared to ultraviolet. © 2014 Elsevier B.V.
Iranian Journal of Physics Research (16826957) 13(3)pp. 283-287
Renewable energy research has created a push for new materials; one of the most attractive material in this field is quantum confined hybrid silicon nano-structures (nc-Si:H) embedded in hydrogenated amorphous silicon (a-Si:H). The essential step for this investigation is studying a-Si and its ability to produce quantum confinement (QC) in nc-Si: H. Increasing the gap of a-Si system causes solar cell efficiency to increase. By computational calculations based on Density Functional Theory (DFT), we calculated a special localization factor, [G Allan et al., Phys. Rev. B 57 (1997) 6933.], for the states close to HOMO and LUMO in a-Si, and found most weak-bond Si atoms. By removing these silicon atoms and passivating the system with hydrogen, we were able to increase the gap in the a-Si system. As more than 8% hydrogenate was not experimentally available, we removed about 2% of the most localized Si atoms in the almost tetrahedral a-Si system. After removing localized Si atoms in the system with 1000 Si atoms, and adding 8% H, the gap increased about 0.24 eV. Variation of the gap as a function of hydrogen percentage was in good agreement with the Tight -Binding results, but about 2 times more than its experimental value. This might come from the fact that in the experimental conditions, it does not have the chance to remove the most localized states. However, by improving the experimental conditions and technology, this value can be improved.
Physical Review B - Condensed Matter and Materials Physics (10980121) 89(7)
Nanocrystals encapsulated within an amorphous matrix are computationally analyzed to quantify the degree to which the matrix modifies the nature of their quantum-confinement power - i.e., the relationship between nanocrystal size and the gap between valence- and conduction-band edges. A special geometry allows exactly the same amorphous matrix to be applied to nanocrystals of increasing size to precisely quantify changes in confinement without the noise typically associated with encapsulating structures that are different for each nanocrystal. The results both explain and quantify the degree to which amorphous matrices redshift the character of quantum confinement. The character of this confinement depends on both the type of encapsulating material and the separation distance between the nanocrystals within it. Surprisingly, the analysis also identifies a critical nanocrystal threshold below which quantum confinement is not possible - a feature unique to amorphous encapsulation. Although applied to silicon nanocrystals within an amorphous silicon matrix, the methodology can be used to accurately analyze the confinement softening of other amorphous systems as well. © 2014 American Physical Society.
Journal of Alloys and Compounds (09258388) 593pp. 235-241
The topological band structure of the CuxAu1- xInTe2 alloys with (x = 0, 0.25, 0.5, 0.75, 1) have been studied by the first principles study in the framework of the density functional theory (DFT) using the generalized gradient approximation (GGA), modified Becke-Johnson (mBJ) and Engel-Vosko generalized gradient approximation (GGA-EV). Our studies show that the topological phase of CuxAu 1-xInTe2 is sensitive to x and type of exchange correlation potentials. The inverted band order occurs with x < 0.25 for mBJ and x < 0.5 for GGA-EV and x > 1 for GGA in band structure. Moreover, the band order of the alloys has been investigated under hydrostatic pressure. The calculated results strength is fitted to several second order polynomial equations for each of approximation. © 2013 Elsevier B.V. All rights reserved.
Chinese Physics B (16741056) 22(12)
In this article, a computational analysis has been performed on the structural properties and predominantly on the electronic properties of the α-CuSe (klockmannite) using density functional theory. The studies in this work show that the best structural results, in comparison to the experimental values, belong to the PBEsol-GGA and WC-GGA functionals. However, the best results for the bulk modulus and density of states (DOSs) are related to the local density approximation (LDA) functional. Through utilized approaches, the LDA is chosen to investigate the electronic structure. The results of the electronic properties and geometric optimization of α-CuSe respectively show that this compound is conductive and non-magnetic. The curvatures of the energy bands crossing the Fermi level explicitly reveal that major charge carriers in CuSe are holes, whose density is estimated to be 0.86 × 1022 hole/cm3. In particular, the Fermi surfaces in the first Brillouin zone demonstrate interplane conductivity between (001) planes. Moreover, the charge carriers among them are electrons and holes simultaneously. The conductivity in CuSe is mainly due to the hybridization between the d orbitals of Cu atoms and the p orbitals of Se atoms. The former orbitals have the dual nature of localization and itinerancy. © 2013 Chinese Physical Society and IOP Publishing Ltd.
Journal of Alloys and Compounds (09258388) 579pp. 360-364
On the basis of ab initio pseudopotential calculations, we study structural, magnetic, dynamical, and mechanical properties of the hypothetical CaC ionic compound in the rock-salt (RS), B2, zinc-blende (ZB), wurtzite (WZ), NiAs (NA), anti-NiAs (NA*), and CrB (B33) structures. It is argued that the ZB, WZ, NA, and RS structures are more ionic while the NAz.ast;, B2, and B33 structures are more covalent systems. As a result of that, the nonmagnetic B33.CaC is the energetically preferred system, while the more ionic structures prefer a ferromagnetic ground state with high Fermi level spin polarization. The observed ferromagnetism in the more ionic systems is attributed to the sharp partially filled p states of carbon atom in the system. In the framework of density functional perturbation theory, the phonon spectra of these systems are computed and the observed dynamical instabilities of the NA. and B2 structures are explained in terms of the covalent bonds between carbon atoms. The calculated Helmholtz and Enthalpy free energies indicate the highest stability of the B33 structure in a wide range of temperatures and pressures. Among the ferromagnetic structures, RS.CaC and ZB.CaC are reported, respectively, to be the most and the least metastable systems in various thermodynamics conditions. Several mechanical properties of the dynamically stable structures of CaC are determined from their phonon spectra. © 2013 Elsevier B.V. All rights reserved.
Journal of Superconductivity and Novel Magnetism (15571947) 26(4)pp. 819-824
We have investigated the structural, electronic, and magnetic properties of MgO nanolayers with two different nanolayer thicknesses (1.5 nm and 1.75 nm) on a Fe substrate. The calculated results in this paper were obtained using the density functional theory (DFT) within the generalized gradient approximation (GGA). The total energies as a function of volume are calculated and thereby the lattice parameters, bulk moduli of MgO nanolayers with two different thicknesses have been calculated. The effects of surface atoms and Fe substrate atoms on physical properties of these nanolayers have been analyzed using the calculated total and partial electron density of states in its ferromagnetic phase. The spin-polarized density of states of MgO shows that this compound is an insulator in the nonmagnetic phase. MgO nanolayers on Fe substrate are metal in the ferromagnetic phase. The magnetic properties of surface atoms and Fe substrate atoms have been investigated and compared with bulk. Furthermore, the effect of hydrostatic pressure on the total and local magnetic moment of these nanolayers has been investigated. © 2012 Springer Science+Business Media New York.
Journal of Superconductivity and Novel Magnetism (15571947) 26(5)pp. 1723-1728
Density functional theory calculations have been performed to study the electronic and magnetic properties of DyNiPb and YNiPb compounds. The total energy calculations indicate that at zero pressure the ferromagnetic and nonmagnetic phases are the most stable phases of the DyNiPb and YNiPb compounds respectively. The Pb atom has a negligible contribution to the magnetic properties of DyNiPb compared to the Dy and Ni atoms. The effect of hydrostatic pressure on the magnetic moment of these compounds is also studied. The calculated results show that the YNiPb compound has zero magnetic moment over the whole pressure range considered (p <20 GPa), while in the DyNiPb compound the total and local magnetic moments at the Dy and Ni atomic sites increase with increasing pressure. Furthermore, I have investigated the electric field gradient (EFG) at different atomic sites of these compounds. The contribution of different orbitals to the EFG shows that the strongest anisotropy in the charge distribution is due to the electrons in the p orbitals. The variation of EFG at different atomic positions of the DyNiPb and YNiPb compounds with pressure is not linear and increases with pressure. © Springer Science+Business Media New York 2012.
Journal of Magnetism and Magnetic Materials (03048853) 341pp. 56-59
Density functional-pseudopotential calculations are employed for more understanding of the exchange interaction in the novel p ferromagnetic CaC and CaN compounds in the rock-salt, zinc-blende, wurtzite and NiAs structures. It is observed that the generalized gradient functional give rises to a half-metallic or nearly half-metallic electronic structure for these systems. Comparing the structural properties in the ferromagnetic and nonmagnetic states clarifies that the bonding properties are almost independent of the exchange interaction in these systems. It is observed that the interatomic exchange interaction in these systems is quite strong and controls the splitting of the spin resolved bond points. The non-local 1-Iartree-Fock based exchange correction is found to enhance the half-metallic behavior of the systems while preserving their equilibrium volume and compressibility. © 2013 Elsevier B.V. All rights reserved.
Journal of Alloys and Compounds (09258388) 549pp. 51-56
The topological band structures of LuPdBixSb1- x (for x = 0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, 1) alloys have been investigated using density functional theory by Wien2k package. The generalized gradient approximation (GGA) and Engel-Vosko generalized gradient approximation (GGA-EV) have been used to obtain accurate the band inversion strength and band order. The calculated results show that LuPdBi xSb1-x alloys for x ≥ 0.25 in GGA and x ≥ 0.375 in GGA-EV are candidates for three dimensional topological insulator or topological metal. Furthermore the effect of hydrostatic pressure on band inversion strength and band order of these alloys has been investigated. © 2012 Elsevier B.V. All rights reserved.
Journal of Superconductivity and Novel Magnetism (15571947) 24(1-2)pp. 603-609
The structural, electronic and magnetic properties of UFe 2 and PuFe 2 have been calculated in the presence and absence of spin-orbit interaction using density-functional theory by the WIEN2K package. The total energy calculations indicate that at zero pressure the ferromagnetic phase is the most stable phase. Both the energy band calculation and the density of states curves indicate that spin-orbit interaction has a considerable effect and cannot be ignored. The magnetic moment calculation within local density approximation (LDA) and generalized gradient approximation (GGA) approaches show that LDA and GGA are not good approaches for this compound. To improve the result, we have calculated the magnetic moment using the GGA + U and LDA + U approaches. The calculation of the magnetic moment as a function of pressure has been investigated. © Springer Science+Business Media, LLC 2010.
Journal of Superconductivity and Novel Magnetism (15571947) 24(1-2)pp. 825-831
In the present work we have investigated the structural, electronic and magnetic properties of MnCo 2Si and MnFeCoSi in bulk and nanolayer using density functional theory. The total energies as a function of volume are calculated and thereby the bulk modulus and their pressure derivatives are determined. The effect of atoms at the surface of these nanolayers has been analyzed using the calculated total and partial electron density of states in its ferromagnetic phase. The spin-polarized density of states show that both bulk MnCo 2Si and MnFeCoSi present a halfmetallicity, which is lost at their nanolayer surfaces. Furthermore, the effects of pressure on the magnetic moment of these compounds in its bulk form are investigated. © Springer Science+Business Media, LLC 2010.
Journal of Superconductivity and Novel Magnetism (15571947) 24(1-2)pp. 879-886
The structural, electronic, and magnetic properties of UAl 3 have been calculated using density functional theory by the Wien2k package within LDA, GGA, LDA+U, and GGA + U approaches. The total energy calculations indicate that at zero pressure the ferromagnetic phase is the most stable phase. The energy band calculation and the density of state curves indicate that the localization of 5f electron and spin orbit coupling have a considerable effect on electronic properties of the UAl 3 compound. The calculations of the electric field gradient, magnetic moment, and optical properties of this compound have been performed under the presence and absence of spin orbit coupling. The contribution of different orbitals to the EFG shows that the strongest anisotropy in the charge distribution is due to the electrons in p orbitals. The electric field gradient and magnetic moment as a function of pressure have been investigated in the presence and absence of spin orbit coupling. © Springer Science+Business Media, LLC 2010.
Journal of Superconductivity and Novel Magnetism (15571947) 24(1-2)pp. 887-893
The electronic and magnetic properties of MnFe xCo 2-xSi alloys have been calculated using density functional theory by Wien2k package, and a ferromagnetic ground state structure has been found for these alloys. The half-metallicity of the MnFe 0.25Co 1.75Si and MnFe 1.75Co 0.25Si is discussed in the light of changes in the orbital hybridization as a result of Fe and Co doping in MnCo 2Si and MnFe 2Si, respectively. The calculated magnetic moment of MnFe xCo 2-xSi alloys shows that the effect of Si atom on magnetic properties of these compounds is negligible compared to Mn, Fe, and Co atoms. The variation of magnetic moment versus x has been investigated. By fitting the nonlinear variation of the calculated magnetic moment versus concentration with third-order polynomials, the magnetic moment bowing factor has been calculated. © Springer Science+Business Media, LLC 2010.
Modern Physics Letters B (02179849) 25(26)pp. 2079-2090
The structural, electronic and magnetic properties of MnXY (X = Ru, Rh and Y = Ga, Ge, Sb) Heusler alloys are studied using density functional theory by the WIEN2k package. These materials are ferromagnetic. Also they have some interesting half-metallic properties. The electron density of states, total and local magnetic moment of these alloys are calculated. We have calculated the effective Coulomb interaction Ueff using the ab initio method. We have compared the magnetic moments of these alloys in GGA and LDA+U with the SlaterPauling rule. Furthermore the effect of hydrostatic pressure on the magnetic moment of these alloys is studied. The calculated results are fitted with a second order polynomial. © 2011 World Scientific Publishing Company.
Physica B: Condensed Matter (09214526) 405(19)pp. 4173-4187
The structural, electronic and optical properties of ZnSxSe 1-x alloys have been investigated using density functional theory by Wien2k package. The exchange correlation potential is treated by the local density approximation (LDA), generalized gradient approximation (GGA), Engel-Vosko generalized gradient approximation (GGA-EV) and GGA-EV plus U (GGA-EV+U). The calculated real and imaginary parts of the dielectric function and the reflectivity of ZnSxSe1-x alloys are in good agreement with the available experimental results particularly in GGA-EV and GGA-EV+U. I have studied the effect of composition on the equilibrium volume, bulk modulus, energy band gap and the static dielectric constant and static reflectivity spectra. Furthermore the effect of hydrostatic pressure on the electronic and optical properties of these alloys has been investigated The first and second order pressure coefficient for the energy band gaps, the static dielectric function and the static reflectivity spectra have been calculated. © 2010 Elsevier B.V. All rights reserved.
Journal of Alloys and Compounds (09258388) 505(2)pp. 698-711
The structural, electronic and optical properties of ZnX and CdX (X = Se, Te and S) are studied using density functional theory by the Wien2k package. The energy band gap, real and imaginary parts of the dielectric function, energy loss function, optical absorption coefficient and reflectivity spectra of these compounds are calculated. The Engel-Vosko approach improves the energy band gaps of ZnX and CdX compounds. The calculated optical parameters are in good agreement with available experimental results, particularly in the Engel-Vosko approach. Furthermore the effect of hydrostatic pressure on the energy band gap, the real and imaginary parts of the dielectric function of these compounds is studied. The first and second order pressure coefficient for the energy band gaps, the static dielectric function and the static reflectivity spectra are calculated. © 2010 Elsevier B.V.All rights reserved.
Physica B: Condensed Matter (09214526) 404(8-11)pp. 1271-1278
I have investigated the behavior of the electric field gradient (EFG) at M site in ThM3 compounds (with M=Sn, In, Si, Ge, Ga, Rh, Pb, Tl) under pressure. I have found that the magnitude of EFG increases with pressure in all compounds. Furthermore I have shown that in ThM3 (with M=In, Ga, Pb, Tl), this increase follows a common trend. Thereby I have reached an equation of state for the EFG in this group. © 2008 Elsevier B.V. All rights reserved.
Journal of Magnetism and Magnetic Materials (03048853) 320(3-4)pp. 503-509
The structural, electronic and magnetic properties of NpSn3 have been calculated using density functional theory by WIEN2K package. The total energy calculations indicate that at zero pressure the anti-ferromagnetic phase is the most stable phase. The magnetic moment calculation within local density approximation (LDA) and generalized gradient approximation (GGA) approaches show that LDA and GGA are not good approaches for this compound. To improve the result, we have calculated the magnetic moment using LDA+U approach. The comparison of total magnetic moment of NpSn3 within LDA+U approach with experimental value shows that the best Coulomb repulsion term for Np atom is achieved with U=2.5 eV and J=0.5 eV. The calculation of orbital and spin magnetic moment as a function of U has been performed. The calculation of orbital magnetic moment as a function of unit-cell volume within LDA+U approach has been performed. © 2007 Elsevier B.V. All rights reserved.
Physica Status Solidi (C) Current Topics in Solid State Physics (16101642) 3(9)pp. 3292-3296
The electronic and magnetic properties of UIn3 have been calculated in the presence of spin orbit coupling using density functional theory (DFT) by the Wien2k package, and an anti-ferromagnetic ground state structure has been found for this compound. The spin and orbital magnetic moments has been found for this compound. The spin and orbital magnetic moment have been calculated, and it has been shown the orbital magnetic moment is directed opposite to the spin magnetic moment. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.
Physica B: Condensed Matter (09214526) 373(1)pp. 16-22
We present a theoretical investigation of structural and electronic properties of the four known structural phases of GaAs (zinc-blende, sc16, cinnabar and Cmcm). We used the full potential linearized augmented plane wave method, within local density approximation, and also within generalized gradient approximation for the exchange correlation potential. The lattice constants, bulk modulus and its pressure derivative are calculated for each of the four phases. The data obtained for the transition pressures between different phases are presented. Band structures and densities of states of the four phases are also given. The results are compared with previous calculations and with experimental results. © 2005 Elsevier B.V. All rights reserved.
Journal of Physics Condensed Matter (09538984) 17(15)pp. 2407-2418
The structural and electronic properties of USn3 have been calculated in the presence and in the absence of spin-orbit interaction using density functional theory by the Wien2k package. Both the energy band calculation and the density of states curves indicate that spin-orbit interaction has a considerable effect and cannot be ignored. Thus the calculation of the electric field gradient (EFG) as a function of pressure has been performed in the presence of spin-orbit coupling. The contributions of different orbitals to the EFG show that the strongest anisotropy in the charge distribution is due to the electrons in p orbitals. © 2005 IOP Publishing Ltd.
International Journal of Modern Physics B (02179792) 19(18)pp. 3049-3061
The actinide compounds exhibit a variety of unusual ground states. These states are dominated by the strong electron-electron correlations that are not included in normal density-functional electronic band-structure calculation with the local density approximation. These correlations are taken into account in the local density approximation +U (LDA+U) method. We have calculated the Coulomb repulsion term U for uranium in USn3 compound, and investigated the total and partial DOS for USn3 using LDA+U method. The LDA+U results for USn3 have been compared with similar results from a ThSn3 model calculation through which the number of 5f electrons outside the U muffin-tin sphere in USn3 has been deduced. We have also calculated the electric field gradient (EFG), which may be regarded as a measure of the asymmetry in charge distribution, at the Sn site in USn3 in LDA, LDA+SO and LDA+SO+U methods, and have shown that the Coulomb repulsion term does not introduce any considerable effect on the electric field gradient at the Sn site. © World Scientific Publishing Company.
