Band Structure Calculations Research Articles

Tl7]7- Clusters in Mixed Alkali Metal Thallides Cs7.29K5.71Tl13 and Cs3.45K3.55Tl7.

Investigations in the ternary system Cs-K-Tl resulted in the unexpected formation of new ternary thallides Cs7.29K5.71Tl13 and Cs3.45K3.55Tl7. Single crystal X-ray structure analyses of both compounds reveal the presence of isolated Tl cluster units. Cs7.29K5.71Tl13 crystallizes in the monoclinic space group C2/c (a = 30.7792(9) Å, b = 11.000(2) Å, c = 14.0291(4) Å, β = 112.676(4)°, Z = 4) and contains [Tl6]6- and [Tl7]7- clusters as thallium subunits. Cs3.45K3.55Tl7 crystallizes in the tetragonal space group I41/a (a = 13.6177(2) Å, c = 25.5573(8) Å, Z = 8) and contains [Tl7]7- clusters exclusively. The formation of Cs7.29K5.71Tl13 is obtained after slow cooling in addition to that of Cs3.45K3.55Tl7 and can be suppressed by quenching the stoichiometric mixture. First dissolution experiments in liquid ammonia suggest thallium and amide as final oxidation products. Full relativistic band structure calculations of Cs4K3Tl7 and Cs8K5Tl13 showed a (pseudo) band gap around EF for both compounds.

Structural, electronic and thermoelectric properties of monolayer TiSe2.

In this work the first-principles calculations of the structural, electronic and thermoelectric properties of monolayer TiSe2 are presented. The optimized lattice parameter of monolayer TiSe2 shows excellent agreement with the experimental value. The computed band structure and density of states calculations predict metallic nature of monolayer TiSe2 with overlapping of 0.44eV between the lowest conduction band and top valance band at high symmetry point M. The position of pseudogap formed by Ti-3d orbitals near the Fermi level confirms the mechanical stability of monolayer TiSe2. Due to the influence of positive strain (tensile strain), the Ti-Se bond length increases and the layer height decreases. The applied tensile strain changes the metallic nature of TiSe2 into a semiconductor with opening of bandgap. It has also been observed that the positions of conduction band minima and valance band maxima change with strain. The charge analysis shows that charge transfer from Ti to Se atom increases when tensile strain is applied, while an opposite trend is observed with compression. The computed thermoelectric coefficientsi.e. Seeback coefficient, power factor and figure of merit are in good agreement with the experimental data.The temperature dependence of these coefficientsis also reported. The density functional theory based calculations are reported employing the PBE-GGA ansatz using the plane wave-pseudopotential method embodied in the Quantum ESPRESSO package. The self-consistent field calculations are performed over a dense Monkhorst-Pack net of 12 × 12 × 1k-points. The energy convergence criteria for the self-consistent field calculation were set to 10-6 Ry/atom with a cutoff energy of 90 Ry. The thermoelectric properties are computed by combining the band structure calculations with the Boltzmann transport equation using Boltztrap2 peckage.

The Substitution of Rare-Earth Gd in BaScCuTe3 Realizing the Band Degeneracy and the Point-Defect Scattering toward Enhanced Thermoelectric Performance.

Zintl compounds have continuously received significant attention, primarily due to their structural characteristics that align with the properties of the electron crystal and phonon glass. In this study, the crystal structure and thermoelectric properties of the quaternary Zintl chalcogenide BaScCuTe3 are investigated. The band structure calculations for BaScCuTe3 reveal a slight energy split of 0.08 eV between the second valence band and the valence band maximum, suggesting the presence of multiband-transport behaviors. Substitution of rare earth Gd for Sc is conducted, which significantly increases the hole concentration from 4.1 × 1019 cm-3 to 8.2 × 1019 cm-3 at room temperature. Meanwhile, the Seebeck coefficient increases because of the participation of the second valence band. A maximum power factor of 6.56 μW/cm·K2 at 773 K is obtained, which is 72% higher than that of the pristine sample. Moreover, the lattice thermal conductivity decreases from 0.57 W/m·K for BaScCuTe3 to 0.48 W/m·K for BaSc0.97Gd0.03CuTe3 at 773 K, owing to the introduction of point-defect scattering. As a result, there is a noteworthy improvement in the thermoelectric figure of merit zT, increasing from 0.44 for the undoped sample to 0.85 for BaSc0.98Gd0.02CuTe3. Considering these findings, BaScCuTe3 exhibits great potential and holds promise for further investigation in the field of thermoelectric materials.

Insights into the Electronic, Optical, and Anti-Corrosion Properties of Two-Dimensional ZnO: First-Principles Study

The electronic, optical, and anticorrosion properties of planer ZnO crystal and quantum dots are explored using density functional theory calculations. The calculations for the finite ZnO quantum dots were performed in Gaussian 16 using the B3LYP/6-31g level of theory. The periodic calculations were carried out using VASP with the plane wave basis set and the PBE functional. The subsequent band structure calculations were performed using the hybrid B3LYP functional that shows accurate results and is also consistent with the finite calculations. The considered ZnO nanodots have planer hexagonal shapes with zigzag and armchair terminations. The binding energy calculations show that both structures are stable with negligible deformation at the edges. The ZnO nanodots are semiconductors with a moderate energy gap that decreases when increasing the size, making them potential materials for anticorrosion applications. The values of the electronic energy gaps of ZnO nanodots are confirmed by their UV-Vis spectra, with a wide optical energy gap for the small structures. Additionally, the calculated positive fraction of transferred electrons implies that electron transfer occurs from the inhibitor (ZnO) to the metal surface to passivate their vacant d-orbitals, and eventually prevent corrosion. The best anti-corrosion performance was observed in the periodic ZnO crystal with a suitable energy gap, electronegativity, and fraction of electron transfer. The effects of size and periodicity on the electronic and anticorrosion properties are also here investigated. The findings show that the anticorrosion properties were significantly enhanced by increasing the size of the quantum dot. Periodic ZnO crystals with an appropriate energy gap, electronegativity, and fraction of electron transfer exhibited the optimum anticorrosion performance. Thus, the preferable energy gap in addition to the most promising anticorrosion parameters imply that the monolayer ZnO is a potential candidate for coating and corrosion inhibitors.

From Molecules to Devices: Insights into Electronic and Optical Properties of Pyridine-Derived Compounds Using Density Functional Theory Calculations.

In this study, we delve into the electronic structure, spectroscopic, and optical properties of five benzo derivatives of pyridine, namely, 5-(4-chlorophenyl)-2-fluoropyridine (1), 2-fluoro-5-(4-fluorophenyl)pyridine (2), 4-(2-fluoropyridin-5-yl)phenol (3), 5-(2,3-dichlorophenyl)-2-fluoropyridine (4), and 5-(5-bromo-2-methoxyphenyl)-2-fluoropyridine (5). Utilizing quantum chemical density functional theory calculations at the B3LYP and Perdew-Burke-Ernzerhof levels of theory combined with the 6-311G(d,p) and 6-311++G(d,p) basis sets, we investigated the electronic and optical characteristics of these compounds. Band structure calculations were conducted for their crystalline structures, revealing a direct band gap varying from 3.018 to 3.558 eV, with the valence band maximum and conduction band minimum located at the G point in the Brillouin zone. The optical properties were analyzed, including the dielectric functions, reflectivity, and refractive index. Notably, reflectivity was found to be minimal in the photon energy range of 0.0-3.0 eV, and the static refractive index, n(0), ranged from 1.55 to 1.70. The research also involved assessing the reactivity of the compounds through calculation of the frontier orbital energy gaps (ΔE), indicating a significant charge transfer and high reactivity. Additionally, we performed frequency analysis to unveil the Fourier-transform infrared spectra of compounds 1-5 at room temperature. Molecular electrostatic potential surfaces of the optimized structures were employed to map the electrophilic and nucleophilic regions of the compounds. This investigation provides a comprehensive understanding of the electronic and optical properties of these pyridine derivatives, shedding light on their potential applications in optoelectronics.

Probing Interlayer Interactions and Commensurate-Incommensurate Transition in Twisted Bilayer Graphene through Raman Spectroscopy.

Twisted 2D layered materials have garnered much attention recently as a class of 2D materials whose interlayer interactions and electronic properties are dictated by the relative rotation/twist angle between the adjacent layers. In this work, we explore a prototype of such a twisted 2D system, artificially stacked twisted bilayer graphene (TBLG), where we probe, using Raman spectroscopy, the changes in the interlayer interactions and electron-phonon scattering pathways as the twist angle is varied from 0° to 30°. The long-range Moiré potential of the superlattice gives rise to additional intravalley and intervalley scattering of the electrons in TBLG, which has been investigated through their Raman signatures. Density functional theory (DFT) calculations of the electronic band structure of the TBLG superlattices were found to be in agreement with the resonant Raman excitations across the van Hove singularities in the valence and conduction bands predicted for TBLG due to hybridization of bands from the two layers. We also observe that the relative rotation between the graphene layers has a marked influence on the second order overtone and combination Raman modes signaling a commensurate-incommensurate transition in TBLG as the twist angle increases. This serves as a convenient and rapid characterization tool to determine the degree of commensurability in TBLG systems.

Investigation of structural, electronic, magnetic, and mechanical stability of a non-trivial topology phase in compound full-Heusler alloys TiHfFeX (X=Al, Ga, In)

In this paper, we present studies relating to the structural, electronic, magnetic and mechanical properties of TiHfFeX ([Formula: see text], Ga, In) full Heusler alloys. We will use the GGA-PBE, TB-mBj, GGA-PBEsol, and GGA-WC approximation implemented in the density functional of the theory as integrated into the Wien2k software. However, the full Heusler alloys studied are considered in the ferromagnetic phase for different structural stabilities of the TiHfFeAl, TiHfFeGa and TiHfFeIn phases. types I, II or III, respectively. Calculation of band structures and total electron density of states shows that these alloys can both exhibit topologically non-trivial semi-metallic characteristics with energy bandgaps of 0.010[Formula: see text]eV, 0.014[Formula: see text]eV and 0.018[Formula: see text]eV. The electronic stability of ’such a Heusler structure will have nothing to do with its mechanical stability. Calculations reveal that the systems exhibit semi-metallic ferromagnetism. The elastic constants and the associated elastic moduli confirm its stability given by different elastic constants namely the Cauchy pressure, Poisson’s ratio, the anisotropy factor, Young’s modulus and the shear modulus.

Computational and experimental approach for investigation of optical properties of single-crystal MnGa2Se4

In the presented work, we propose a systematic investigation of the electronic and optical properties of MnGa2Se4 by combining the spectroscopic ellipsometry carried out at room temperature in the spectral range of 1–4 eV and density functional theory (DFT) calculations. Ellipsometric measurements were collected at an incidence angle between 60° and 75° with a 5° step. The optical direct gap energies of MnGa2Se4 were estimated from the linear extrapolation of the absorption coefficients that were verified by band structure calculation. DFT calculation of the imaginary part ɛ shows that first critical point occurs at 2.46 eV and represents the direct optical transition at Γ point. The total magnetic moment of compound is 3.38 mB. The major contribution in total magnetic moment is due to 3 d state of Mn atoms.

Predictive analysis of a new FeVTe alloy from first principles: An excellent choice for thermoelectric applications

To predict the thermoelectric (TE), magnetic, and electrical properties of the novel half-Heusler FeVTe as well as its dynamical, mechanical, and structural stability, this investigation makes use of the WIEN2K code and the FP-LAPW technique, which relies on density functional theory (DFT). The exchange-correlation potential in this analysis is handled using the GGA-PBE approximation. According to our predicted results, we can draw the conclusion that this compound exhibits stability in the ferromagnetic (FM) type I phase and reveals a total magnetic moment of unity. From the computed band structure, FeVTe unveils half-metallic (HM) behaviour, showing metallic features in the spin-up direction and a semiconductor character in the downspin direction with an indirect bandgap of 1.27 eV. The alloy complies with the Slater-Pauling law based on the predicted spin-polarized magnetic moments (MMs). Also, the results obtained for the elastic constants suggest that this material is ductile, anisotropic, and mechanically stable. Moreover, this compound demonstrates a remarkable figure of merit at room temperature and elevated temperatures, suggesting its potential as promising material for thermoelectric applications.

The effects of Zn and Yb co-dopants on the electronic, radiation shielding, structural, thermal and spectroscopic properties of hydroxyapatite

This work presents a comprehensive investigation of the electronic properties of hydroxyapatite (HA) doped with zinc (Zn) and ytterbium (Yb). Four different compositions, namely 0.33Zn-0.33Yb-HA, 0.33Zn-0.66Yb-HA, 0.66Zn-0.33Yb-HA, and 0.66Zn-0.66Yb-HA, were studied using Density of States (DOS) and band structure calculations. The computed band gap values for each composition were determined to be 4.3097 eV, 4.1324 eV, 4.2527 eV, and 4.2088 eV, respectively. The observed decrease in the band gap energy from 0.33Zn-0.33Yb-HA to 0.66Zn-0.66Yb-HA signifies a significant impact of the dopant composition on the electronic properties of the material. Furthermore, the inclusion of ytterbium in the HA matrix resulted in the formation of a distinct band and peak in the density of states. This indicates the emergence of specific energy levels associated with Yb, suggesting a distinct influence on the electronic structure of the material. These findings provide valuable insights into the tunability of the electronic properties of HA through controlled doping with Zn and Yb. Such knowledge is crucial for tailoring materials with desired electronic characteristics, thus holding promise for various applications in electronic devices and biocompatible coatings. The as-modeled structures were synthesized via a wet chemical route. Fourier transform infrared (FTIR), Raman, and X-ray diffraction (XRD) analyses verified the formation of the HA structure for each sample. Differential thermal analysis (DTA) results showed that all the as-prepared samples were thermally stable. The negligible mass losses were detected for all the samples in the thermogravimetric analysis (TGA) measurements. The addition of both co-dopants affected crystal structure related parameters and decreased the crystallinity and cell viability.

Fabrication of MoSe2/Bi3O4Br Z-scheme heterojunction with enhanced photocatalytic performance

Exploring a Z-scheme heterojunction photocatalyst with efficient charge separation and outstanding redox ability is necessary but very challenging. MoSe2 has received much attention as a co-catalyst due to its excellent optical properties. Herein, First-principles density functional theory (DFT) was employed for theoretical calculations of the energy band structure of Bi3O4Br, revealing crossed energy band structures with MoSe2, indicating favorable conditions for heterojunction formation. A solvothermal method was then used to synthesize MoSe2/Bi3O4Br heterostructure photocatalysts with a 2D/2D layered configuration. Characterization via SEM, TEM, DRS, XPS, BET, EIS, and PL confirmed that the MoSe2/Bi3O4Br heterostructure exhibited a larger specific surface area, more active sites, lower impedance, and reduced carrier recombination rate compared to pure Bi3O4Br and MoSe2. These features are advantageous for photocatalytic reactions. The optimized 2.5% MoSe2/Bi3O4Br photocatalyst demonstrated superior performance, achieving nearly 100% photodegradation of RhB under 90 min of simulated sunlight, with an apparent rate constant k value 7.57 times higher than that of Bi3O4Br. The composite photocatalyst exhibited excellent cycling stability over five experiments without significant reactivity attenuation. Finally, a plausible Z-scheme photocatalytic mechanism for MoSe2/Bi3O4Br heterojunctions is proposed based on experimental findings. This study provides new insights for exploring the construction of wide-band semiconductor heterojunctions.

DFT calculations of the structural, elastic, and electronic properties of (Bi1−xFex)2Te3 chalcogenides

The crystal structure and elastic and electronic properties of (Bi1−xFex)2Te3 were studied by first-principles calculations within the Density Functional Theory (DFT) scheme. We found that at zero GPa, the lattice parameters for Bi2Te3 are in good agreement with the available experimental and theoretical data. As Fe replaces bismuth, the lattice parameter a increases while c decreases, changing the unit cell volume. According to Born’s structural stability criterion, the system is mechanically stable. Poisson’s ratio suggests a change from brittle to ductile behavior for (Bi1−xFex)2Te3 as iron increases. Also, Poisson’s ratio indicates that there is an ionic-covalent bond for x = 0.00 and behave as a metal as iron content increases. Vickers hardness decreases its value as Fe is introduced in the compound. Band structure calculations show that the results with spin orbit coupling (SOC) and without SOC are in good agreement with the experimental results. With SOC, a direct band gap at the Γ point is obtained with Eg = 0.138 eV concerning the 0.226 eV obtained without SOC. An evident modification of crystal structure in (Bi1−xFex)2Te3 shows a consistent trend, indicating a significant impact of iron incorporation on the structural properties. The electronic properties show a significant transformation with the introduction of iron, Bi2Te3 is characterized by a band gap, through iron doping the electronic structure shows a complete elimination of the band gap, marking a transition from semiconductor towards a conductor-like behavior. Density of states analysis provided insight into these changes, illustrating a modulation of electronic properties dependent on iron content.

Electronic Properties of Chiral IrGe4 Studied by Angle Resolved Photoemission Spectroscopy and Band Structure Calculation

Electronic Properties of Chiral IrGe₄ Studied by Angle Resolved Photoemission Spectroscopy and Band Structure Calculation

Exploring the Structural, Elastic, and Optoelectronic Properties of ScCuO3 via Density Functional Theory Approach

A thorough analysis of the structural, elastic, electronic, and optical properties of ScCuO3 perovskite is conducted using density functional theory. The compound's structural and mechanical stabilities are established under pressure. The values of Pugh's ratio (B/G) and the Zener anisotropy factor indicate that ScCuO3 displays ductile behavior and elastic anisotropy under varying pressures. The metallic behavior of ScCuO3 is confirmed by its electronic band structure, which shows that a few valence bands intersect the Fermi level. The Cu‐3d and O‐2p orbitals overlap near the Fermi level, which is found from the density of states diagram. It is also proclaimed that the Cu‐3d states strongly hybridized with O‐2p states are observed under applied pressure. Various optical properties (dielectric function, photoconductivity, absorption coefficient, loss function, reflectivity, and refractive index) are also analyzed. The compound has the highest reflectivity and is found in the low‐energy region, making it suitable as a coating material for reducing solar heating. The absorption spectra and optical conductivity indicate the metallic nature of ScCuO3, which is supported by the calculations of the electronic band structure. The current study explores the potential applications of ScCuO3 in various optoelectronic devices.

The germanides ScTGe2 (T = Fe, Co, Ru, Rh) – crystal chemistry, 45Sc solid-state NMR and 57Fe Mössbauer spectroscopy

Abstract The TiMnSi2-type (space group Pbam) germanides ScTGe2 (T = Fe, Co, Ru, Rh) were synthesized from the elements by arc-melting. Single crystals were grown by annealing sequences of the arc-melted buttons in an induction furnace. The structures of ScFeGe2, ScRuGe2 and ScRhGe2 were refined from single-crystal X-ray diffraction data. In ScRuGe2, the ruthenium atoms have distorted octahedral germanium coordination (242–268 pm Ru–Ge). Three trans-face-sharing octahedra form a sub-unit which is condensed via common edges in c direction and connected via common corners with four adjacent blocks, forming a three-dimensional [RuGe2 type] substructure. The two crystallographically independent scandium sites have coordination numbers 15 (Sc1@Ge8Ru4Sc3) and 17 (Sc2@Ge7Ru6Sc4). Electronic band structure calculations for ScCoGe2 and ScRuGe2 show a net charge transfer from the scandium to the transition metal and germanium atoms, leading to a description with polyanionic networks Sc δ+[TGe2]δ−. The two crystallographically independent Sc sites are easily distinguishable by 45Sc magic-angle spinning (MAS)-NMR spectroscopy. Isotropic chemical shift values and nuclear electric quadrupolar interaction parameters were deduced from an analysis of the triple-quantum (TQ)-MAS NMR spectra. The electric field gradient parameters deduced from these experiments are in good agreement with quantum-chemical calculations using the Wien2k code. Likewise, the two crystallographically independent iron sites in ScFeGe2 could be discriminated in the 57Fe Mößbauer spectra through their isomer shifts and quadrupole splitting parameters: δ = 0.369(1) mm s−1 and ∆E Q = 0.232(2) mm s−1 for Fe1 and δ = 0.375(2) mm s−1 and ∆E Q = 0.435(4) mm s−1 for Fe2 (data at T = 78 K).

Evolution of the Electronic and Excitonic Properties in 2D Ruddlesden–Popper Perovskites Induced by Bifunctional Ligands

Abstract2D Ruddlesden–Popper metal‐halide perovskites exhibit structural diversity due to a variety of choices of organic ligands. Incorporating bifunctional ligands in such materials is particularly intriguing since it can result in novel electronic properties and functions. However, an in‐depth understanding of the effects of bifunctional ligands on perovskite structures and, consequently, their electronic and excitonic properties, is still lacking. Here, n = 1 2D perovskites built with organic ligands containing ─CN, ─OH, ─COOH, ─phenyl (Ph), and ─CH3 functional groups are investigated using ultraviolet and inverse photoemission spectroscopies, density functional theory calculations, and tight‐binding model analyses. The experimentally determined electronic gaps of the ─CN, ─COOH, ─Ph, and ─CH3 based perovskites exhibit a strong correlation with the in‐plane Pb─I─Pb bond angle, while the ─OH based perovskite deviates from the linear trend. Based on the band structure calculations, this anomaly is attributed to the out‐of‐plane dispersion, caused predominantly by significant interlayer electronic coupling that is present in ─OH based perovskites. These results highlight the complex and diverse impacts of organic ligands on electronic properties, especially in terms of the involvement of strong interlayer electronic coupling. The impact of the bifunctional ligands on the evolution of the exciton binding energy is also addressed.

Ab-initio calculation of magnetic properties of doped methylammonium lead chloride

ABSTRACT Magnetic properties of 3d transition metal ion doped methylammonium lead chloride (MAPbCl3) have been studied by ab-initio calculations in the framework of density functional theory. The study of spin–spin interactions reveals that doping (about 2%) of Ti, V, Cr, Mn and Fe at the Pb site of MAPbCl3 shows stable ferromagnetic ordering along with the half-metallic behaviour. 3d orbital electrons of the dopants are primarily responsible for the origin of the magnetic moment and the remaining part comes from the p-d exchange interaction between the 3d orbital electrons of the dopants and the 6p orbital electrons of Pb in the vicinity of the doping position. Additionally, the band structure calculations suggest that the doped system shows n/p-type semiconducting behaviour. Ferromagnetism, along with semiconducting behaviour in transition metal ion-doped MAPbCl3, will be suitable for spintronic applications.

Structural, Electronic, Mechanical and Optical Properties of RhZrZ (Z = As, Sb) Half‐Heusler Compounds: First‐Principles Calculations

In this study, density functional theory (DFT) as it is implemented in the Quantum Espresso simulation package was employed to investigate the structural, electronic, mechanical and optical properties of RhZrZ (Z = As, Sb) half‐Heusler compounds. Results reveal that both the two compounds are most stable in α phase. Analysis of mechanical properties shows that the compounds are ductile in nature and mechanically stable. Calculations of band structure and density of states indicated that they are semiconductors with RhZrAs direct and RhZrSb indirect band gap. Furthermore, the investigation of the optical properties reveals that there is a high absorption coefficient and low electron energy loss in visible and some ultraviolet energy spectrum indicating that these compounds are potential candidates for optoelectronic applications.

Extremely large magnetoresistance with coexistence of a nontrivial Berry phase in Nb0.5Ta0.5P: an experimental and theoretical study

We synthesized Nb0.5Ta0.5P, exhibiting XMR at low temperatures with charge carrier compensation up to 50 K. SdH oscillations reveal multiple Fermi pockets and non-zero Berry phase. SOC effects were analyzed via band structure calculations.

Investigation of adsorption properties of SF6 decomposed gases (SO2 and SO2F2) on pristine and Ti-decorated SWCNT surfaces: A DFT study

DFT calculations were employed to investigate the adsorption of gases produced from SF6 decomposition (SO2 and SO2F2) on pristine and Ti- -decorated single-walled carbon nanotubes (Ti-(8,0) SWCNT). All structures were relaxed and their structural and electronic properties were investigated before and after gas adsorption on the surface of the nanotubes. (Ti-(8,0) SWCNT) was found to have high chemisorption sensitivity to Ti, SO2F2 and SO2 adsorptions on its surface. The electronic properties of (8,0) SWCNT were altered from semiconductor to metallic upon decoration with Ti, as demonstrated by the calculated band structures and the density of states (DOS). SO2F2 and SO2 adsorption on the surface of (Ti-(8,0) SWCNT) from different sides transformed the conductor (Ti-(8,0) SWCNT) into a semiconductor nanotube. To more carefully study the nature of adsorption, partial density of states (PDOS) calculations were also made. Additionally, Ti decoration induced a magnetization of approximately 2.61 ?B in (8,0) SWCNT, which disappeared after gas adsorption.