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Flat electronic bands in condensed matter provide a rich avenue for exploring novel quantum phenomena. Here, we report an optical spectroscopy study of a topological hourglass semimetal Nb3SiTe6 with the electric field of the incident light parallel to its crystalline ab -plane. The ab -plane optical conductivity spectra of Nb3SiTe6 single crystals exhibit a remarkable peak-like feature around 1.20 eV, which is mainly contributed by the direct optical transitions between the two ab-initio -calculation-derived flat bands along the momentum direction Z – U. Our results pave the way for investigating exotic quantum phenomena based on the flat bands in topological hourglass semimetals. [ABSTRACT FROM AUTHOR]

Flat electronic bands in condensed matter provide a rich avenue for exploring novel quantum phenomena. Here, we report an optical spectroscopy study of a topological hourglass semimetal Nb3SiTe6 with the electric field of the incident light parallel to its crystalline ab -plane. The ab -plane optical conductivity spectra of Nb3SiTe6 single crystals exhibit a remarkable peak-like feature around 1.20 eV, which is mainly contributed by the direct optical transitions between the two ab-initio -calculation-derived flat bands along the momentum direction Z – U. Our results pave the way for investigating exotic quantum phenomena based on the flat bands in topological hourglass semimetals. [ABSTRACT FROM AUTHOR]

The kagome lattice has garnered significant attention due to its ability to host quantum spin Fermi liquid states. Recently, the combination of unique lattice geometry, electron–electron correlations, and adjustable magnetism in solid kagome materials has led to the discovery of numerous fascinating quantum properties. These include unconventional superconductivity, charge and spin density waves (CDW/SDW), pair density waves (PDW), and Chern insulator phases. These emergent states are closely associated with the distinctive characteristics of the kagome lattice's electronic structure, such as van Hove singularities, Dirac fermions, and flat bands, which can exhibit exotic quasi-particle excitations under different symmetries and magnetic conditions. Recently, various quantum kagome materials have been developed, typically consisting of kagome layers stacked along the z -axis with atoms either filling the geometric centers of the kagome lattice or embedded between the layers. In this topical review, we begin by introducing the fundamental properties of several kagome materials. To gain an in-depth understanding of the relationship between topology and correlation, we then discuss the complex phenomena observed in these systems. These include the simplest kagome metal T 3 X, kagome intercalation metal TX, and the ternary compounds AT 6 X 6 and RT 3 X 5 (A = Li, Mg, Ca, or rare earth; T = V, Cr, Mn, Fe, Co, Ni; X = Sn, Ge; R = K, Rb, Cs). Finally, we provide a perspective on future experimental work in this field. [ABSTRACT FROM AUTHOR]

Searching for the dispersionless flat band (FB) in quantum materials, especially in topological systems, becomes an interesting topic. The kagome lattice is an ideal platform for such exploration because the FB can be naturally induced by the underlying destructive interference. Nevertheless, the magnetic kagome system that hosts the FB close to the Fermi level (E F) is exceptionally rare. Here, we study the electronic structure of a kagome magnet LuMn6Sn6 by combining angle-resolved photoemission spectroscopy and density functional theory calculations. The observed Fermi-surface topology and overall band dispersions are similar to previous studies of the X Mn6Sn6 (X = Dy, Tb, Gd, Y) family of compounds. We clearly observe two kagome-derived FBs extending through the entire Brillouin zone, and one of them is located just below E F. The photon-energy-dependent measurements reveal that these FBs are nearly dispersionless along the kz direction as well, supporting the quasi-two-dimensional character of such FBs. Our results complement the X Mn6Sn6 family and demonstrate the robustness of the FB features across this family. [ABSTRACT FROM AUTHOR]

Recently, the newly synthesized septuple-atomic layer two-dimensional (2D) material MoSi2N4 (MSN) has attracted attention worldwide. Our work delves into the effect of vacancies and external electric fields on the electronic properties of the MSN/graphene (Gr) heterostructure using first-principles calculation. We find that four types of defective structures, N-in, N-out, Si and Mo vacancy defects of monolayer MSN and MSN/Gr heterostructure are stable in air. Moreover, vacancy defects can effectively modulate the charge transfer at the interface of the MSN/Gr heterostructure as well as the work function of the pristine monolayer MSN and MSN/Gr heterostructure. Finally, the application of an external electric field enables the dynamic switching between n-type and p-type Schottky contacts. Our work may offer the possibility of exceeding the capabilities of conventional Schottky diodes based on MSN/Gr heterostructures. [ABSTRACT FROM AUTHOR]

Knowledge of the physical properties of a material is crucial to realising its practical technological applications. In this regard, a study related to phase stability, transition pressure, electronic properties, optical properties, and thermal properties of GaAs, GaN, as well as their mixed ternary alloys GaN0.25As0.75, GaN0.5As0.5 and GaN0.75As0.25 is presented. The study is performed by employing a “full-potential-linearized augmented plane wave plus local-orbital (FP-L(APW + lo)) approach framed within the density functional theory (DFT)” and recognized within WIEN2k computational code. The results of the phase stability show that the GaNxAs1–x alloys are stable for all compositions in the zinc blende phase (B3), except for x = 1, whereas the structure corresponding to the x = 1 composition is found to be more stable in the wurtzite (B4) phase. The physical properties of the more stable phases corresponding to each composition are explored. The pressure-induced phase transition is also investigated, corresponding to each composition. The electronic and optical properties are investigated using the “Tran–Blaha modified Becke–Johnson (mBJ)” potential approach. To explore the thermal properties, the "quasi-harmonic Debye model" approach is employed. Our calculated results of the absorption coefficients and optical band gap show that these alloys could be appropriate candidates for applications in solar cells and optoelectronic devices. [ABSTRACT FROM AUTHOR]

We propose a new generalized Su–Schrieffer–Heeger model with hierarchical long-range hopping based on a one-dimensional tetratomic chain. The properties of the topological states and phase transition, which depend on the cointeraction of the intracell and intercell hoppings, are investigated using the phase diagram of the winding number. It is shown that topological states with large positive/negative winding numbers can readily be generated in this system. The properties of the topological states can be verified by the ring-type structures in the trajectory diagram of the complex plane. The topological phase transition is strongly related to the opening (closure) of an energy bandgap at the center (boundaries) of the Brillouin zone. Finally, the non-zero-energy edge states at the ends of the finite system are revealed and matched with the bulk–boundary correspondence. [ABSTRACT FROM AUTHOR]

In this work, using first-principle calculations based on the density functional theory (DFT), the structural and electronic properties of the ternary compound ZnSnAs2 are presented. An accurate ab-initio plane-wave pseudopotential method within meta-generalised gradient approximation (MGGA) has been performed for bulk ZnSnAs2 chalcopyrite semiconductor. Additionally, the modified Becke–Roussel exchange potential has also been used to improve the underestimated DFT-calculated band gap. DFT-MGGA computations reveal that ZnSnAs2 chalcopyrite has direct band gaps of 0.66 and 0.67 eV. A proper investigation of the electronic structure of the studied chalcopyrite is helpful for photonic devices. [ABSTRACT FROM AUTHOR]

In this study, we have explored the structural, electronic and thermal properties of La x Sc 1 - x N ternary alloys in rock-salt structure using the full-potential linearised augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). To calculate the exchange-correlation energy and potential, we have used the Wu–Cohen generalised gradient approximation and the modified Becke–Johnson. We investigated the effect of composition on lattice parameters, bulk modulus and band gap. The variation of the calculated lattice constant with lanthanum composition is practically linear and shows a small deviation of the obtained results from Vegard's law. Moreover, the effect of thermal macroscopic properties was also investigated employing the quasiharmonic Debye model, which takes into account the lattice vibrations. We have found a good accord between our results, the experimental data and previous theoretical results available in the literature for the binary compounds which can be a support for the ternary alloys in the future. [ABSTRACT FROM AUTHOR]

In this paper attempts to predict the presence of structural phase transition in some nitrides from zinc-blende (B3) to rock-salt (B1) structures when put under pressure using an interaction potential model (IIPM), which includes Coulomb interactions, three-body interaction (TBI) based or charge transfer effect and overlap repulsive interaction operative up to second neighbour. The transition takes places at 3, 6.7 and 36 GPa, accompanied by sudden drops in volumes of 15.31%, 2.35% and 5.11% in ZnN, MnN and TcN, respectively. For investigating electronic properties we have used the full-potential linearized augmented plane wave method based on the density functional theory. The computed electronic band structures confirm the metallic behaviour of these compounds. The second-order elastic constants have also been examined at zero and high pressure and we observed that these values increase monotonically under the influence of pressure. Our outcomes are, in general, in good agreement with the other theoretical results. [ABSTRACT FROM AUTHOR]

The structural, electronic, and magnetic properties of half-Heusler alloys (HHAs) MnTiX (X = Si, Ge, Se, Te) are studied using full potential linearized augmented plane wave (FP-LAPW) method as implemented in Wien2k code which is a well-known code to investigate the physical properties of materials. The geometry optimization calculations for ferromagnetic (FM) and anti-ferromagnetic phases have been performed in order to determine the most stable phase of these materials. The results revealed that FM phase is the most stable, and further calculations (spin band structures and density of states) are carried for FM phase. The obtained results of band structures and density of states show that all considered alloys have half-metallic (HM) behavior with 100% spin polarization at the Fermi level. Furthermore, the exchange coupling of s-d and p-d exchange have also been discussed in detail for these materials. [ABSTRACT FROM AUTHOR]

The optical spectra of gyrotropic α-Hg3S2Cl2 polymorph were calculated for the first time to give a deep insight into its band structure. The exchange–correlation potential was treated with the generalized gradient approximation and modified Becke–Johnson potential (MBJ) to improve the accuracy of electronic structure calculation. The detailed analysis of the low-energy electronic states near the Fermi level was conducted. The main contributions of the sulfur and chlorine p states are located at the top of the valence band, while the S/p and Hg/s states give main contribution to the bottom of the conduction band. The direct optical band gap of 3.19 eV is at the Г-points of Brillouin zone. The value of direct optical transitions, which was calculated by MBJ method, agrees very well with the experimental report on diffuse reflectance spectra. The reported structural and optical properties of α-Hg3S2Cl2 polymorph make it a potentially interesting compound for nonlinear optical applications. [ABSTRACT FROM AUTHOR]

The structural, electronic and mechanical properties of heavy rare earth (DyX, X = S, Se and Te) chalcogenide compounds, which crystallize in B1 phase, have been investigated for the first time using FP-LAPW method within the framework of density functional theory. The local spin density approximation with Hubbard parameter (LSDA + U) has been used for exchange–correlation potentials. The calculated ground-state properties such as lattice constants, bulk moduli and pressure derivatives are in good agreement with previously reported results. Further, magnetic moments for these compounds have also been calculated. The metallic nature of these compounds was confirmed by electronic band structures and density of states. Furthermore, to meet the applications of such materials, elastic constants and mechanical properties such as Young modulus, shear modulus, Poisson ratio, anisotropic factor, B/G ratio and Cauchy's pressure have also been calculated. DyS shows brittle nature, while DySe and DyTe show ductile nature under ambient conditions. [ABSTRACT FROM AUTHOR]

SnS2 is an important disulfide having many excellent properties for application. Here we carried out a firstprinciples study of its electronic, elastic and lattice dynamic properties. The band structure calculated by the HSE06 functional indicates that SnS2 is an indirect band gap semiconductor with a gap of 2.16 eV. Calculated partial density of states and the Mulliken charges imply that SnS2 is an ionic-covalent compound. Studies unveil that SnS2 is mechanically and dynamically stable, but it is easy to crack along the c-axis. Phonons at its Brillouin zone center were assigned by group theory analysis and their frequencies were computed. Investigation of its Born effective charges and dielectric constants reveals that ions have a larger dielectric contribution than electrons in the ab plane, but they almost have no contribution along the c direction. [ABSTRACT FROM AUTHOR]

SnS2 is an important disulfide having many excellent properties for application. Here we carried out a firstprinciples study of its electronic, elastic and lattice dynamic properties. The band structure calculated by the HSE06 functional indicates that SnS2 is an indirect band gap semiconductor with a gap of 2.16 eV. Calculated partial density of states and the Mulliken charges imply that SnS2 is an ionic-covalent compound. Studies unveil that SnS2 is mechanically and dynamically stable, but it is easy to crack along the c-axis. Phonons at its Brillouin zone center were assigned by group theory analysis and their frequencies were computed. Investigation of its Born effective charges and dielectric constants reveals that ions have a larger dielectric contribution than electrons in the ab plane, but they almost have no contribution along the c direction. [ABSTRACT FROM AUTHOR]

In this article, we present the first-principles calculations for electronic and optical properties of AlSb and GaSb in the zinc blende phase using density functional theory. These calculations were carried out using the full potential-linearized augmented plane wave method embedded in WIEN2K package. Perdew–Burke–Ernzerhof and modified Becke–Johnson approximations with and without addition of spin–orbit interaction (SOI) effect were taken as exchange-correlation potentials. With SOI effect, we found that AlSb has an indirect bandgap (Г − Δmin) of 1.66 eV and GaSb has a direct bandgap (Г–Г) of 0.812 eV. These results are in good agreement with experimental data and are far better than the theoretical results published elsewhere. We also calculated the dielectric functions, refractive indexes, reflectivities, energy loss functions, optical conductivities and absorption coefficients as a function of frequency in order to investigate the optical responses of AlSb and GaSb. Also, the calculated critical point energies with SOI effect are consistent with the experimental results. [ABSTRACT FROM AUTHOR]

First-principle computations on structural and electronic properties of cubic rare-earth ErX 3 ( X = Ga , In and Sn) intermetallic compounds have been accomplished using the full-potential linearised augmented plane wave (FP-LAPW) method within the framework of density functional theory (DFT). For the exchange correlation, we used local spin density approximation (LSDA) plus Hubbard parameter U (LSDA + U) approach because of the strong on-site Coulomb repulsion between the localised RE-4f states. Calculated ground-state properties such as lattice constant (a 0) and other parameters with exchange correlation functional are found compatible with the experimental results. The electronic properties have been determined in terms of band structures, total and partial density of states (DOSs) and Fermi surfaces, which demonstrate the metallic behaviour of all the compounds. Also, the effect of Hubbard potential on this is discussed in detail. The bonding descriptions of these compounds have also been evaluated from charge density difference plots, which display the presence of metallic and mixed covalent–ionic bonding. The determined magnetic moments explain the ferromagnetic behaviour of these compounds. [ABSTRACT FROM AUTHOR]

A pseudopotential approach is used to study the lattice and elastic properties of the wide band-gap GaN at zero and high pressures up to 120 kbar. When the pressure is 0 kbar, our findings are generally in agreement with the data reported in the literature. The pressure dependence of lattice constant, polarity, transverse effective charge, elastic constants and their related mechanical parameters, and microhardness has been examined and discussed. Our results show that all these features exhibit a monotonic behaviour against pressure. Upon compression up to 120 kbar, our results suggest that the material in question remains mechanically stable with higher stiffness, becomes more resistant to the deformations or deflections and its chemical bond and rigidity become stronger. [ABSTRACT FROM AUTHOR]

The full-potential linearized-augmented plane wave calculations based on density functional theory are performed to study the structural, electronic, optical and thermodynamic properties of scandium chalcogenides ScX (X = S, Se, Te) and their ternary alloys at equilibrium as well as under pressure. The revised Perdew–Burke–Ernzerhof generalized gradient approximation (GGA) is used to calculate the structural properties. The electronic and optical properties are calculated employing the GGA and the modified Becke–Johnson (mBJ) approaches. Moreover, the calculated lattice parameters agree well with the experiment results. The structure NaCl-type (B1) of the scandium chalcogenides undergoes under pressure a structural phase transition to CsCl-type (B2) and ZnS-type (B3). The binary and ternary alloys indicate a metallic behavior using GGA and mBJ scheme. The interband contribution to the optical properties is investigated by calculating the dielectric parameters ε1(ω), ε2(ω) and the index of refraction n(ω). A quasi-harmonic Debye model is applied to calculate the thermal properties. [ABSTRACT FROM AUTHOR]

The first principles calculations of structural and magnetic properties of the Heusler material Mn2NiAl, have been studied using a full potential linearized augmented plane wave (FP-LAPW) within the density-functional theory (DFT). The phase stability of the cubic austenitic (L21) structure for Mn2NiAl in both Cu2MnAl (Fm3 m space group) and Hg2CuTi (F43 m space group) type of structures with ferromagnetic and antiferromagnetic states, has been treated by applying the generalized gradient approximation proposed by Wu and Cohen (WC-GGA) alongside with the martensitic structure of Mn2NiAl. The analysis of phase stability, cohesive energy and the calculated formation enthalpy of Mn2NiAl reveal that the ferromagnetic MnMnNiAl is the most stable type of structure. Moreover, the calculated lattice parameters are found to be in good agreement with theoretical data. The variation of total magnetic moments MT(μB), MMn (μB), MNi (μB) and MAl (μB) in Mn2NiAl with pressure at varying temperature (0, 273 and 344 K), have been calculated. [ABSTRACT FROM AUTHOR]

The density of energy states were obtained in a quantizing magnetic field at different temperature and for nonquadratic dispersion law. The dependence of the density of energy states on temperature in quantizing magnetic fields is studied with the nonquadratic dispersion law. The continuous spectrum of the energy density of states at low temperature is transformed into discrete Landau levels. The theory of the temperature dependence of the oscillation Shubnikov–de Haas in semiconductors with a nonparabolic dispersion law is constructed, taking into account the thermal broadening of the Landau levels. The cyclotron effective mass of the electrons is determined from the Shubnikov–de Haas data. The theoretical results are compared with experimental data in Bi1.99Tl0.01Se3. [ABSTRACT FROM AUTHOR]

Germanium is an important semiconductor having abundant phases of scientific interest. In this work, we studied the structural, electronic, vibrational, elastic and thermal conductivity properties of a tetragonal germanium via first-principles calculations. The results indicate that it is dynamically stable and there is a breathing vibrational mode at its Brillouin zone center. It is a weak metal according to the GGA-based calculation, but an indirect bandgap semiconductor with a gap of 0.24 eV based on the HSE06-functional calculation. According to the calculations performed by the HSE06 functional, both positive and negative hydrostatic pressures can first alter the band gap to be direct and then metallic. The crystal is mechanically stable but anisotropic. Its hardness is predicted to be 8.2 GPa, slightly lower than that of cubic diamond-type Ge. Based on the calculated phonon dispersion curves, its thermal conductivity as a function of temperature is predicted, giving a value of about 13.5 W m-1 K-1 at 300 K. [ABSTRACT FROM AUTHOR]

The elastic, mechanical and thermal properties of isostructural and isoelectronic nonmagnetic REPt3 (RE = Sc, Y and Lu) intermetallic compounds, which crystallize in AuCu3-type structure, are studied using first principles density functional theory based on full potential linearized augmented plane wave method. The calculations are carried out within PBE-GGA, WC-GGA and PBE-sol GGA for the exchange correlation potential. Our calculated ground state properties such as lattice constant (ao), bulk modulus (B) and its pressure derivative (B′) are in good agreement with the available experimental and other theoretical results. We first time predict the elastic constants for these compounds using GGA approximations. All the compounds are found to be ductile in nature in accordance with Pugh’s criteria. The computed electronic band structures show metallic character of these compounds. The charge density plot and density of states of these compounds reveals that the chemical bond between RE and Pt is mainly ionic. The elastic properties including Poisson’s ratio (σ), Young’s modulus (E), shear modulus (GH) and anisotropy factor (A) are also determined using the Voigt-Reuss-Hill averaging scheme. The average sound velocities (vm), density (ρ) and Debye temperature (θD) of these REPt3 compounds are also estimated from the elastic constants. We first time report the variation of elastic constants, elastic moduli, sound velocities and Debye temperatures of these compounds as a function of pressure. [ABSTRACT FROM AUTHOR]

We investigated the emission of visible light from perovskite zirconate CaZrO 3 and BaZrO 3 nanocrystals (NCs) implanted with Cu ions. The CaZrO 3 and BaZrO 3 NCs were synthesized by using the combustion method, and were post-annealed at various temperatures for the purpose of changing their structural properties. The annealed NCs were subjected to Cu-ion implantation with ion doses from 0 up to 1 × 10 16 particles/cm 2 . The XRD patterns of the NCs indicated that the Cu-ion implantation did not affect the structural properties of the NCs. In their photoluminescence spectra, we identified sizable yellow and green/blue emissions, which were caused by the Cu-ion implantation, in addition to a violet emission which was due to structural defects of the host compound. As the Cu-ion dose and annealing temperature were increased, the implantation-induced emission became stronger from both the CaZrO 3 and BaZrO 3 NCs. In comparison with the case of the previously studied implanted SrZrO 3 NCs, the intensity and the spectral shape of the Cu-ion emission were found to depend strongly on the identity of the divalent cation (A in AZrO 3 ) in close relation to the structural properties of the host zirconate. Analysis of absorption coefficient spectra of the NC samples showed that their band gaps were not affected by Cu-ion implantation. From the measured PL spectra, we calculated the CIE color coordinates, and found that colors of the light emitted from the NCs changed from violet-blue to white (close to yellow). [ABSTRACT FROM AUTHOR]

Using the coherent potential approximation within full-potential local orbital minimum-basis method, we have performed a systematic investigations on the possible martensitic transformation, electronic and magnetic properties for Ti2CoGa1-xCux system. Results show that the system has a potential martensitic transformation and can be synthesized in experiment with exception of Ti2CoCu alloy due to their negative formation energy. Calculated total magnetic moment are in good agreement with the Slater-Pauling rule Mt = Zt - 18, thus the system is ferromagnetic half-metallic material except for Ti2CoCu, which is also confirmed by density of states with the band gap at the Fermi level, a nonmagnetic behavior is observed for Ti2CoCu alloy. In addition, the potential martensitic transition from cubic to non-modulated tetragonal transformation illustrates more stability of martensitic phase with respect to cubic one. Such behavior can be explained by the hybridizations between the d orbitals. [ABSTRACT FROM AUTHOR]

First principles calculations of band energy, density of states and dielectric function of K1.75(NH4)0.25SO4 single crystals in Pnma structure is performed in the framework of density functional theory. In order to describe the exchange-correlation interaction the general gradient approximation and local density approximation are used. Character and genesis of main energy bands of the crystal are discussed and comparison with data set for K2SO4 isomorphic crystal performed. The influence of partial isomorphic substitution K→ NH4 found itself mainly in altering the bottom of conduction band and decrease of band gap value. From the dielectric functions dependences, the refractive indices dispersion and absorption coefficient spectra are deduced. Obtained refractive indices satisfactorily agree with experimental data in the visible spectrum region. [ABSTRACT FROM AUTHOR]

Ab initio calculations based on the density functional theory within the fullpotential linearized augmented plane wave method were carried out to investigate the structural stabilities of the different crystallographic phases, the pressure-induced phase transition and the electronic properties of the platinum carbide (PtC) compound. The zinc-blende (ZB), rock-salt (RS), cesium chloride (CsCl), wurtzite (WZ), nickel arsenide (NiAs), lead monoxide (PbO) and the tungsten carbide (WC) phases were considered. The exchange and correlation potential was treated by the generalized-gradient approximation using the Perde-Burke-Ernzerhof parameterization. The thermodynamic properties such as variation of the bulk modulus, lattice constant, heat capacity, thermal expansion and Debye temperature versus pressures and temperatures are investigated. The band structure results show the metallic character of the PtC compound in all the considered phases and the present study also shows that the PtC compound crystallizes in the ZB phase at ambient conditions. The theoretical transition pressures from the ZB to RS for the NiAs, PbO and CsCl transformations were also computed. [ABSTRACT FROM AUTHOR]

The first-principle density functional theory (DFT) calculations were employed to investigate the electronic structures, magnetic properties and half-metallicity of Ti2IrZ(Z = B, Al, Ga, and In) Heusler alloys with AlCU2text {Mn}$$ - and $$\text {CuHg}_{2}\text {Ti}$$ -type structures within local density approximation and generalised gradient approximation for the exchange correlation potential. It was found that $$\text {CuHg}_{2}\text {Ti}$$ -type structure in ferromagnetic state was energetically more favourable than $$\text {AlCu}_{2}\text {Mn}$$ -type structure in all compounds except $$\text {Ti}_{2}\text {IrB}$$ which was stable in $$\text {AlCu}_{2}\text {Mn}$$ -type structure in non-magnetic state. $$\text {Ti}_{2}\text {IrZ}$$ (Z $$=$$ B, Al, Ga, and In) alloys in $$\text {CuHg}_{2}\text {Ti}$$ -type structure were half-metallic ferromagnets at their equilibrium lattice constants. Half-metallic band gaps were respectively equal to 0.87, 0.79, 0.75, and 0.73 eV for $$\text {Ti}_{2}\text {IrB}$$ , $$\text {Ti}_{2}\text {IrAl}$$ , $$\text {Ti}_{2}\text {IrGa}$$ , and $$\text {Ti}_{2}\text {IrIn}$$ . The origin of half-metallicity was discussed for $$\text {Ti}_{2}\text {IrGa}$$ using the energy band structure. The total magnetic moments of $$\text {Ti}_{2}\text {IrZ}$$ (Z $$=$$ B, Al, Ga, and In) compounds in $$\text {CuHg}_{2}\text {Ti}$$ -type structure were obtained as $$2\mu _{\mathrm{B}}$$ per formula unit, which were in agreement with Slater-Pauling rule ( $$M_{\mathrm{tot}} =Z_{\mathrm{tot}}-$$ 18). All the four compounds were half-metals in a wide range of lattice constants indicating that they may be suitable and promising materials for future spintronic applications. [ABSTRACT FROM AUTHOR]

Gibbs script within the all-electron full potential linearized augmented plane wave (FP-LAPW) method has been used to calculate pressure-induced phase transition at zero temperature for selected phases. The calculation exhibits that CdSe is stable at wurtzite phase whereas CdSe0.75Te0.25, CdSe0.5Te0.5, CdSe0.25Te0.75and CdTe are stable at cubic phase. This prediction is consistent with experimental work of Schenk and Silber at˂ 800 °C except for CdSe0.75Te0.25. We found that increasing the Te content for both phases of ternary CdSe1−xTexalloys decreases the optimized energy and bulk modulus, hence leads to decrease hardness, while it increases the optimized volume. The density functional theory (DFT) calculation within generalized gradient approximation (PBE-GGA) and the two-dimensional search of equation of state for wurtzite phase predict a possible pressure-induced phase transition from cubic to wurtzite phase for the ternary CdSe0.5Te0.5, CdSe0.75Te0.25and CdTe at pressures of about 13.6, 1.9 and 10.6 (GPa) with corresponding volume collapses at the phase-transition boundary of about 181.115 and 180.525, 203.839 and 203.485 and 203.337 and 202.692 (bohr3/atom), respectively. However, one-dimensional search of equation of state for wurtzite phases predicts a possible pressure-induced phase transition at pressures 14.5, 1.9 and 11.4 for CdSe0.5Te0.5, CdSe0.75Te0.25and CdTe, respectively. [ABSTRACT FROM PUBLISHER]

Functionalizing the edges of graphene nanoribbons (GNR) plays a vital role to alter their electronic properties. In present work, the effect of sp 2 ∕ sp 3 edge functionalization of zigzag GNR (ZGNR) via H/F is investigated to reveal their structural stability and spin dependent electronic properties. Depending upon the way of functionalization, nanoribbons under considerations are categorized in three groups viz. Group A: one edge is sp 2 functionalized while other edge is sp 3 functionalized, Group B: both the edges are sp 3 functionalized and Group C: both edges are sp 3 functionalized, however, number of H and F atoms are different. All the group A and group C structures settled in magnetic ground state while group B nanoribbons are all nonmagnetic except F 2 -ZGNR- H 2 which prefers ferromagnetic state. Further, it is noticed that F functionalization enhances the stability and is equivalent to p-type doping of nanoribbon along with affecting the electronic properties significantly. Interestingly, for selective structures, magnetic ground state has been obtained and the observed magnetic stabilization is found to be greater than room temperature thermal excitations which ensures the potential of considered ZGNR for practical applications. Present findings provide a viable way for tailoring the spintronic properties of ZGNR and absolute shifting of Fermi level which can play a crucial role for designing future nano-devices. [ABSTRACT FROM AUTHOR]

Applicability of three different thermodynamic models based on classical (Qi model) as well as quantum approach (Lu et al. and Jiang et al. models) have been discussed to search out the exact description of band gap variation with size in semiconducting nanowires. All considered models showed an increment in the band gap as diametric size of the wire decreases. To study band gap and the band edge shift of nanowires, a novel approach has been proposed by incorporating shape effect with size in Jiang et al. model due to its accuracy or consistency with the experimental results. Hence a unified model without any adjustable parameter has been established for studying the combined effect of size and shape on band edges shift [∆E (D), ∆E (D)] and the band gap expansion [∆E (D)] of the semiconducting nanowires. Present study reveals that for small-sized nanowires band gap expansion and edge shift is not only governed by size but also varies with the cross-sectional shape. Band gap expansion and edge shift showed rising behavior due to the enhancement in surface area. [ABSTRACT FROM AUTHOR]

The structural, electronic, elastic, dynamic and optical properties of the ternary chalcopyrite compound MgGeSb were studied by using the density functional theory (DFT) framework for different exchange-correlation functionals. The obtained equilibrium structural parameters are in good agreement with the available theoretical result. After considering the electronic band structure and electronic density of states (DOS) calculation; this compound is a semiconductor as suggested in the previous work. However; all considered functionals underestimate considerably the electronic band gap energies compared with the experimental results. We have predicted single-crystal elastic constants and related properties such as Young's modulus, Poisson ratio, shear modulus and bulk modulus. Optical properties such as the dielectric function, refractive index, extinction index have been calculated in the range of 0-20 eV. The obtained results can facilitate an assessment of possible applications of MgGeSb. [ABSTRACT FROM AUTHOR]

The electronic and optical properties of the rock-salt, CsCl-type, zinc-blende and wurtzite phases of TiN have been calculated by First-Principles study for relaxed and under pressure conditions. Calculations are based on the density functional theory and full potential augmented plane waves method by Generalized Gradient Approximation. The optical transitions in zero pressure are derived from the density of states and dielectric function. In addition, various optical characters, such as reflectivity, refraction and extinction indices, under positive and negative pressures are compared and contrasted. It is found that all mentioned phases of TiN are elastically stable and exhibit a rising trend in their plasmonic frequencies by increasing the pressure imposed on. [ABSTRACT FROM AUTHOR]

Using the spin-polarized relativistic Korringa–Kohn–Rostoker method, we study the electronic and magnetic properties of Fe2NiAs compound with the Hg2CuTi structure. Electronic calculations reveal the d–d orbital hybridization taking an important role in the compound. The calculated magnetic moments, which contain the spin and orbital moments, are primarily carried by Fe atoms located in A and B sites. The orbital moment of Fe2NiAs system is rather small due to the cause of orbital quenching, implying a weak spin–orbit coupling. Simultaneously, we also study the influence of lattice constant on the magnetic moment, it is found that both spin and orbital moments are sensitive to the changes of lattice constants, i.e., the moments become larger as the expansion of lattice constant, indicating the enhancement of spin–orbit coupling effect. In addition, we investigate the magnetic interactions between the constituents to obtain the Heisenberg exchange coupling parameters. It is noted that the interactions are dominated by a strong exchange between Fe atoms. Finally, we acquire the Curie temperatures of Fe2NiAs compound under different lattice constants by using mean field approximation. [ABSTRACT FROM AUTHOR]

We investigated the emission properties of Bi 3.25 La 0.75 Ti 3 O 12 polycrystals and (K 0.5 Na 0.5 )(Mn 0.005 Nb 0.995 )O 3 thin films with strong gamma (γ)-ray irradiation by using temperature dependent photoluminescence spectroscopy. At the lowest temperatures, sizable visible emissions were identified for the γ-ray irradiated samples as well as un-irradiated ones. In both kinds of compounds, the visible emission intensity tended to be increased without changing the spectral shape, as the γ-ray dose increased. This indicates that the γ-ray irradiation should increase all kinds of already-existing defects evenly, without preferring the formation of some particular type of defect. [ABSTRACT FROM AUTHOR]

In this study, we have investigated the electronic and optical properties of half-Heusler NiXSn (X = Zr, Hf) compounds under pressure by means of first principles calculations. The generalized gradient approximation is used to model exchange-correlation effects. We have estimated a transition from indirect band gap to direct band gap at 50 and 127 GPa for NiZrSn and NiHfSn, respectively. We have also plotted the static dielectric constant versus pressure for both compounds. The obtained results are in agreement with the available experimental and theoretical data. [ABSTRACT FROM AUTHOR]

The paper theoretically investigates the peculiarities of energy diagram of asymmetric graded-band-gap superlattices with linear coordinate dependences of band gap and electron affinity. For calculating the energy diagram of asymmetric graded-band-gap superlattices, linearized Poisson's equation has been solved for the two layers forming a period of the superlattice. The obtained coordinate dependences of edges of the conduction and valence bands demonstrate substantial transformation of the shape of the energy diagram at changing the period of the lattice and the ratio of width of the adjacent layers. The most marked changes in the energy diagram take place when the period of lattice is comparable with the Debye screening length. In the case when the lattice period is much smaller that the Debye screening length, the energy diagram has the shape of a sawtooth-like pattern. [ABSTRACT FROM AUTHOR]

We report the results of an ab initio study of the electronic, optical and thermodynamic properties of the LiBaP and LiSrP compounds using the pseudopotential plane-wave method within the framework of the density functional theory with the GGA-PBEsol. The calculated equilibrium structural parameters are in good agreement with the available experimental data. The energy band dispersions along the high symmetry directions in the k-space and the density of states diagrams are computed and analyzed. The obtained energy bands show that both examined crystals are indirect band gap semiconductors. The chemical bonding character is examined via electron density map plots. The optical properties are predicted for an incident radiation in an energy range up to 15 eV, and the origins of the main peaks in the optical spectra are discussed in terms of the calculated electronic band structure. We have also predicted the temperature and pressure dependencies of the unit-cell volume, thermal expansion coefficient, heat capacity, Debye temperature and Grüneisen parameter. [ABSTRACT FROM AUTHOR]

Structural, electronic, elastic, optical, and vibrational properties of ternary half-Heusler compounds HfXSb (X = Co, Rh, Ru) were studied with means of ab initio calculations based on the density functional theory. The calculated lattice constants were in good agreement with the available data. The electronic structure and corresponding density of states (DOS) were also calculated. Indirect band gaps were observed for HfCoSb and HfRhSb. Due to some valence bands crossing the Fermi level, HfRuSb has metallic character. In addition to the electronic structure, elastic and optical properties, phonon dispersion curves and phonon DOS were calculated. A detailed comparison was made between these three half-Heusler compounds. [ABSTRACT FROM AUTHOR]

Structural and electronic properties of α, β, δ and ε polymorphs of BeH are studied. The effect of pressure on these properties is also seen. Investigations are carried out using the linear combination of atomic orbitals method. The lattice parameters, computed by coupling total energy calculations with the Murnaghan equation of state for the four crystals, are overall in agreement with the experimental data and other calculations. Enthalpy-pressure diagram indicates structural phase transitions α → β, α → δ, α → ε, β → δ, β → ε, and δ → ε to occur at 8.75, 12.75, 18.34, 39.53, 55.57 and 76.60 GPa respectively. Electronic band structure and density of states from PBE-GGA show that all polymorphs have wide bandgap. However, quantitative and qualitative agreement of the bandgap from hybrid calculations is observed with available GW data in α-BeH. Therefore bandgaps from hybrid calculations are also proposed. In the three polymorphs the bandgap decreases slowly with pressure. Beyond 100 GPa, the β structure exhibits overlap of bands at the Γ point. [ABSTRACT FROM AUTHOR]

InTe, SnAs and PbSb formally have unusual valence states, In 2+ , Sn 3+ and Pb 3+ . All of them have B1 crystal structure at some pressure range. They are candidates of the valence-skip compound, which may have negative effective Coulomb interaction U eff < 0. Negative-U Hubbard model is known to show charge-density wave or superconductivity in some parameter region. In fact, SnAs becomes superconducting at ambient pressure. InTe has a kind of charge-density wave at ambient pressure, and it becomes superconducting at high pressure. We investigated their electronic structures by ab-initio calculations, and calculated the number of s-electrons at the cation site. We found that InTe is favorable to emerge valence skip, while PbSb is not favorable for valence skip. SnAs is between these two. These findings well agree with the experimental results. [ABSTRACT FROM AUTHOR]

Structural, electronic and optical properties of inorganic aerosols, including ammonium nitrate NHNO and sodium nitrate NaNO have been investigated using the pseudo-potential plane wave scheme in the frame of generalized gradient approximation. The geometrical parameters of the unit cell have been fully optimized and are in good agreement with the experimental data. The electronic structures show that NHNO and NaNO have a direct gap of 3.21 eV and indirect band gap of 2.92 eV, respectively. The optical constants, including the dielectric function, refractive index, extinction coefficient, reflectivity and energy-loss spectra have been calculated and discussed. NHNO and NaNO absorb in the ranges [75-350] and [60-380] nm respectively. [ABSTRACT FROM AUTHOR]

We investigate the spin–orbit coupling (SOC) effects on the electronic structures and semi-classic transport coefficients of half-Heusler ANiB (A = Ti, Hf, Sc, Y; B Sn, Sb, Bi) by using generalized gradient approximation (GGA). Calculated results show that SOC splits the valence bands at high symmetry Γ point, and modifies the outline of Γ-centered valence bands, which has remarkable effects on the electron transport properties. Thermoelectric properties are performed through solving Boltzmann transport equations within the constant scattering time approximation. It is found that the compounds containing Sn atom have larger power factor in p-type doping than ones in n-type doping, and it is just the opposite for compounds containing Sb and Bi elements. The SOC has obvious detrimental influence on power factor in p-type doping, while has a negligible effect in n-type doping. These can be understood by considering the effects of SOC on the valence bands and conduction bands. The maximum power factors (MPF) are extracted in n-type and p-type doping with GGA and GGA + SOC, and the MPF at 300 K with SOC is predicted to be about 4.25%∼ 44.13% smaller than that without SOC in the case of p-type doping for ANiB (A = Ti, Hf, Sc, Y; B Sn, Sb, Bi). Therefore, it is crucial to consider SOC effects for theoretical analysis in the case of p-type doping in half-Heusler compounds composed of heavy elements. [ABSTRACT FROM AUTHOR]

We predict that a given transition-metal salt as, for example, a K2CuCl4·2H2O-type compound, can behave as an electrical conductor in the paramagnetic case. In fact, we determine the electrical conductance in a salt of this type. This conductance is found to be quantised in agreement with previous well-known results. Related mathematical expressions in the context of superexchange interaction are obtained. In addition, we determine the corresponding (macroscopically viewed) current density and the associated electron wave functions. [ABSTRACT FROM AUTHOR]

In this study, the structural, elastic, electronic, and bonding nature of AgZn in B2 structure under pressure have been investigated by performing first principles calculations using density functional theory. The exchange-correlation potentials were treated within the generalized gradient approximation. The calculated quantities agree well with the available results. The electronic properties, such as band structure and density of states reveal that AgZn is metallic in nature with a large overlap at the Fermi level. The single-crystal elastic stiffness constants of AgZn are investigated using the stress-strain method. Present results for elastic constants show that AgZn is mechanically stable. The chemical bonding is interpreted by calculating the density of states and electron density distribution analysis. AgZn has ionic bonding characteristic. [ABSTRACT FROM AUTHOR]