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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
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)
Advanced Quantum Technologies (25119044) 6(7)
This study presents a thorough analysis of the electronic structures of the TaPxAs1−x series of compounds, which are of significant interest due to their potential as topological materials. Using a combination of first principles and Wannier-based tight-binding methods, this study investigates both the bulk and surface electronic structures of the compounds for varying compositions (x = 0, 0.25, 0.50, 0.75, 1), with a focus on their topological properties. By using chirality analysis, (111) surface electronic structure analysis, and surface Fermi arcs analysis, it is established that the TaPxAs1−x compounds exhibit topologically nontrivial behavior, characterized as Weyl semimetals (WSMs). The effect of spin–orbit coupling (SOC) on the topological properties of the compounds is further studied. In the absence of SOC, the compounds exhibit linearly dispersive fourfold degenerate points in the first Brillouin zone (FBZ) resembling Dirac semimetals. However, the introduction of SOC induces a phase transition to WSM states, with the number and position of Weyl points (WPs) varying depending on the composition of the alloy. For example, TaP has 12 WPs in the FBZ. The findings provide novel insights into the electronic properties of TaPxAs1−x compounds and their potential implications for the development of topological materials for various technological applications. © 2023 The Authors. Advanced Quantum Technologies published by Wiley-VCH GmbH.
Sadat nourizadeh, S. ,
Vaez, A. ,
Vashaee, D. Physical Review Materials (24759953) 7(11)
This paper undertakes a comprehensive examination of the electronic and topological properties of triclinic enantiomorphic NbPxAs1-x alloys (x =0, 0.25, 0.50, 0.75, 1) belonging to the space group P1, through first-principles and Wannier-based tight-binding analyses. Our paper reveals band inversion coupled with a distinctive fourfold band crossing near the Fermi energy, attributed to hybridization among Nb-d orbitals. Intriguingly, NbPxAs1-x alloys exhibit nontrivial topological features even without spin-orbit coupling (SOC), primarily due to band inversion. Upon incorporating SOC, the fourfold band crossings transition into gapped bands, bifurcating into pairs of Weyl points with distinct chiralities. These Weyl points possess linear dispersion, categorizing the alloys as type-I topological Weyl semimetals. Additionally, SOC induces the emergence of Fermi arcs in the (111) surface states of the first Brillouin zone, connecting Weyl points of opposite chiralities. The findings establish NbPxAs1-x alloys as promising candidates for applications in topological materials, while enriching the understanding of topological phases and their correlations with electronic structure. © 2023 American Physical Society.
Setayandeh, S.S. ,
Gould, T. ,
Vaez, A. ,
Gray, E. International Journal of Hydrogen Energy (03603199) 46(1)pp. 943-954
Density functional theory is increasingly used to predict and understand the properties of hydrogen storage materials. Many such calculations have been performed for various real and hypothetical palladium hydrides, yet despite excellent agreement on electron band structures, significant disparities persist in relation to phonon band structures and critical matters such as dynamic stability of alternative structures. Some disparities may arise because of differing computation approaches between researchers. Therefore in this work a systematic approach was followed to compare calculated electron and phonon band structures for four palladium hydrides: PdH and Pd3VacH4 (the superabundant vacancy phase) assuming that octahedral (oct) or tetrahedral (tet) lattice interstices are occupied by H, with six commonly used calculation schemes based on the local density approximation and the generalised gradient approximation, within the harmonic approximation. Of the twenty-four combinations tested, seven are new to the literature. Excellent agreement was found between the calculation schemes for the electron band structures of all four crystal structures. The position regarding phonons is much less satisfactory, however, and highlights the sensitivity of phonon properties to the calculated lattice constants. None of the calculation schemes could reproduce the measured phonon energy gap of PdH(oct) and it is necessary to include anharmonicity of the H potential to obtain realistic results. The calculated lattice constants of PdH(tet) were larger than any observed in experiments, although the structure is dynamically stable. All six calculation schemes predicted dynamic instability for Pd3VacH4(oct), although the calculated lattice constant agreed with the estimated zero-temperature experimental value. This structure requires new calculations accounting for anharmonicity. The calculated lattice constant for Pd3VacH4(tet) was larger than any experimental value, so this alternative, while dynamically stable, is certainly not observed. © 2020 Hydrogen Energy Publications LLC
Setayandeh, S.S. ,
Gould, T. ,
Vaez, A. ,
Mclennan, K. ,
Armanet, N. ,
Gray, E. Journal of Alloys and Compounds (09258388) 864
The partial atomic volume of hydrogen, vH, is a fundamentally important thermodynamic parameter of interstitial metal hydrides in which dissociated H occupies interstices in the metal lattice. Such an important property should be able to be reliably calculated by a suitable theory or model in order to explain and understand its origin. In practice, vH is typically obtained by means of ab initio calculations founded on density functional theory (DFT), where the equilibrium lattice constant at zero temperature is found by minimising the Born-Oppenheimer energy. While the absolute lattice constants calculated in this way depend quite strongly on the DFT scheme employed, the present work showed that vH is rather robust against differing calculational approaches, thus making a meaningful comparison of theory and experiment possible. Comparing vH for PdnH (0
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).
Indian Journal of Physics (09731458) 93(6)pp. 733-738
Functionalized graphene sheets have attracted increasing attention due to their novel micro-/nano-electromechanical applications. In this paper, the aggregation of the gold nano-clusters on the defected graphene sheet is studied by using the molecular dynamics simulation method. It is shown that a model defected graphene with randomly distributed vacancies can affect the formation and aggregation of the Au nano-clusters on the graphene sheet. It is found that the Au nano-clusters agglomerate on the pristine parts of the surface rather than on the defected parts. In addition, the results show that increasing the temperature amplifies the above result and varies the Au nano-cluster sizes. Moreover, it is observed that the aggregation of Au clusters changes the surface roughness. The results presented here would help to design more efficient functionalized graphene-based electronic devices. © 2018, Indian Association for the Cultivation of Science.
Computational Condensed Matter (23522143) 21
The AlNi intermetallic compound is one of the most promising engineering materials for high temperature applications. Unfortunately, this compound has low tensile ductility at high temperature which limit its functional applications. We show that alloying the AlNi compound with the Cr or V will improve its tensile ductility and therefore its industrial applications. In this paper, the structural, electronic, elastic and thermodynamic properties of Al1-xZxNi (Z = Cr, V and x = 0, 0.125, 0.25) alloys have been studied by the first principles calculations in the framework of density functional theory. The calculated formation energy and cohesive energy of the alloys show that, all alloys have stable structures. The valence charge density distribution study reveals that, chemical bonds between the Z and Ni atoms in the alloys have the nature of covalent, which improve the brittleness of the AlNi alloys. The calculated Pugh's ratio (or the Poisson's ratio), shear and bulk modules show that, the increasing of hardness by increasing the x. Moreover, the ductility of the alloys decreased when the value of x is nonzero. The calculation results show that the Pugh's (Poisson's) ratio is higher than 1.75 (0.26), indicating a ductile nature of these alloys. Furthermore, thermodynamic properties of the alloys including Grüneisen parameter, thermal expansion coefficient, bulk modulus, Debye temperature and constant volume heat capacity have been investigated and discussed under different pressures and temperatures. © 2019 Elsevier B.V.
International Journal of Modern Physics B (02179792) 32(11)
In this paper, thermodynamic and elastic properties of the AlNi and AlNi3 were investigated using density functional theory (DFT). The full-potential linearized augmented plane-wave (APW) in the framework of the generalized gradient approximation as used as implemented in the Wien2k package. The temperature dependence of thermal expansion coefficient, bulk modulus and heat capacity in a wide range of temperature (0-1600 K) were investigated. The calculated elastic properties of the compounds show that both intermetallic compounds of AlNi and AlNi3 have surprisingly negative Poisson's ratio (NPR). The results were compared with other experimental and computational data. © 2018 World Scientific Publishing Company.
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.
Physica E: Low-Dimensional Systems and Nanostructures (13869477) 103pp. 164-170
In this paper, topological phase and optical properties of bulks and nanolayers (NLs) of the ScNiX (X = Ga and In) half-Heusler compounds have been studied. The calculations have been done based on the density functional theory in the framework of the Wien2k package. The generalized gradient approximation was used for the exchange-correlation functional. Electronic structures and density of states of the bulks and NLs of the compounds show that, they are non-magnetic and metal. It is found that, the bulks of compounds don't have topological phase, but the NLs of compounds have topological phase. Thus, the NLs of both compounds are topological metals. Important optical properties of these compounds were acquired. The results show that, there is optical anisotropy in the NLs, between the in-plane (x) and out-of-plane (z) directions. The absorptions of the bulks and NLs of the compounds are high in the UV range. © 2018 Elsevier B.V.
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.
Journal of Superconductivity and Novel Magnetism (15571947) 28(3)pp. 949-954
The electronic, magnetic, and optical properties of TbN and ErN nanolayers in the presence of spin orbit coupling using density functional theory using the WIEN2k package are investigated. The stable phase of TbN and ErN bulk using generalized gradient approximation (GGA) approach is studied. The total and partial electron density of states of ErN and TbN nanolayers with two different thicknesses in ferromagnetic phase within GGA and Engel–Vosko GGA (GGA_EV) approaches is calculated. The total and local magnetic moments of these nanolayers are studied. The calculated magnetic moment at Er atomic position of ErN nanolayer is larger than the corresponding value at Tb atomic position of TbN nanolayer. Furthermore, the real and imaginary parts of the dielectric function and the reflectivity and absorption spectra of these nanolayers within GGA_EV approach are studied. © 2014, Springer Science+Business Media New York.
Journal of Computational and Theoretical Nanoscience (15461955) 12(9)pp. 2437-2441
Molecular dynamics simulations, based on many-body inter-atomic potentials, have been performed to investigate the propagation of a Mode-I (edge) crack in a two-dimensional (2D) (111) plane of a random alloy of Pd and different percentage of Ir atoms. The Sutton-Chen many-body potential was used to simulate all inter-atomic interactions. We show that, fluctuations in the crack velocity, which lead to the phenomenon of crack branching, are also present in this alloy. Furthermore, it is found that as the percentage of Ir atoms increases, the critical stress for the initiation of crack propagation is increased, and the fluctuations in the crack velocity make their appearance sooner. © 2015 American Scientific Publishers All rights reserved.
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.
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.
Kharatha, M. ,
Vaez, A. ,
Hasan rozatian, A.S. Molecular Physics (00268976) 111(24)pp. 3726-3732
Gas sensing is one of the most promising applications for graphene. Using molecular dynamics simulation method, adsorption isotherm of xenon (Xe) gas on defected and perfect graphene is studied in order to investigate sensing properties of graphene for Xe gas. In this method, first generation of Brenner many-body potential is used to simulate the interaction of carbon-carbon (C) atoms in graphene, and Lennard-Jones two-body potential is used to simulate interaction of Xe-Xe and Xe-C atoms. In the simulated systems, adsorption coverage, radial distribution function, heat of adsorption, binding energy and specific heat capacity at constant volume are calculated for several temperatures between 90 K and 130 K, and various pressures. It was found that both of the defected and perfect graphene could be introduced as very good candidates for adsorption of Xe gas. © 2013 Taylor and Francis Group, LLC.
Journal of Superconductivity and Novel Magnetism (15571947) 26(4)pp. 1339-1341
The magnetic properties of Mnx Fe1-x NiSi (x=0,0.25,0.5,0.75,1) alloys are studied using density functional theory and the WIEN2k package. The exchange correlation potential is treated by generalized gradient approximation (GGA). The total energy calculations of these alloys confirm the stability of the ferromagnetic phase as compared to a nonmagnetic phase. The total magnetic moment is not a linear function of x. By increasing x, it increases and then decreases. The peak position of the magnetic moment is near x=0.75. © 2012 Springer Science+Business Media New York.
Journal of Computational and Theoretical Nanoscience (15461955) 9(8)pp. 1059-1062
In this letter we performed ab initio calculations on the perfect and defected (5, 5) single walled carbon nanotube (SWNT) with Stone Wales (SW) defects. The band structure, density of state (DOS) and wave functions of a long (5, 5) carbon nanotube are calculated. Our results show that, due to the SW defect, the Band structure and DOS of SWNT changed significantly and the metallic behavior of (5, 5) o-SWNT changed to a semiconductor behavior. This confirms that SW defects can drastically change the electronic structures and transport properties of SWNTs. Copyright © 2012 American Scientific Publishers.
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.
Chemical Physics Letters (00092614) 437(4-6)pp. 233-237
Molecular dynamics (MD) simulation is used to compute the adsorption isotherms of xenon (Xe) gas on defected open ended single-walled nanotubes (o-SWNT). We perform a simulation based on a many-body interatomic Brenner potential with a two-body interatomic Lennard-Jones (LJ) potential. Adsorption isotherms of Xe on (10, 10) o-SWNT for several temperatures, between 95 and 130 K, are measured. Adsorption coverage, isosteric heat, and binding energy were calculated at various temperatures and pressures and compared with the same properties for the perfect (10, 10) o-SWNT. It is shown that adsorption occurs both inside and outside of an o-SWNTs. © 2007 Elsevier B.V. All rights reserved.
