Band Structure Calculations Research Articles

Heusler-based topological quantum catalyst Fe2VAl with obstructed surface states for the hydrogen-evolution reaction

Topological materials are widely esteemed for their surface metallic states and remarkable carrier mobility, making them effective catalysts for heterogeneous processes. This study showcases the outstanding properties of Fe2VAl, an experimentally prepared compound that enjoys a Cu2MnAl-type Heusler structure. It specifically highlights the presence of robust obstructed surface states on the (001) surface and the outstanding catalytic effectiveness of the compound in electrochemical hydrogen evolution processes (HER). The band structure calculation in this work shows that it is an obstructed atomic semimetal with a pseudo-gap of -0.088 eV (nearly -0.1 eV). These findings align with the previous optical conductivity measurements conducted at low temperatures, which also showed a similar pseudo-gap. This work suggests that the easily prepared Fe2VAl compound may be an excellent topological quantum material for topological catalysis.

Fermi-liquid behavior of nonaltermagnetic RuO2

The presence of magnetism in potentially altermagnetic RuO2 has been a subject of intense debate. Using broadband infrared spectroscopy combined with density-functional band-structure calculations, we show that the optical conductivity of RuO2, the bulk probe of its electronic structure, is best described by a nonmagnetic model. The sharp Pauli edge demonstrates the presence of a Dirac nodal line lying 45 meV below the Fermi level. An excellent match between the experimental and plasma frequencies underpins the weakness of electronic correlations. The intraband part of the optical conductivity indicates Fermi-liquid behavior with two distinct scattering rates below 150 K. Fermi-liquid theory also accounts for the temperature-dependent magnetic susceptibility of RuO2 and allows a consistent description of this material as a paramagnetic metal. Published by the American Physical Society 2025

New Layered Boride NiPtB2-x (x = 0.5) with a Ternary Derivative Structure of MoB.

A novel ternary boride, NiPtB2-x (x = 0.5), was obtained by argon-arc melting of the elements followed by annealing at 750 °C. It exhibits a new structure type with the space group Imma (a = 2.9835(3) Å, b = 3.0470(3) Å, c = 15.3843(3) Å; Z = 4; single-crystal X-ray data) and displays distinct layers of condensed [BNi6] and [BPt6] (and [Pt6]) trigonal prisms with mutually perpendicular axes. Atoms of Pt and Ni from adjacent layers interlink to form empty tetragonal pyramids and tetrahedra. Two boron atom positions form two orthogonal zigzag chains; however, one boron position exhibits a partial boron occupancy. Considering B-deficiency, the platinum boride substructure in NiPtB2-x quantitatively corresponds to a trigonal prismatic slab in the Pt2B structure, while the nickel boride partial structure is consistent with the CrB-type NiB binary. Cell parameters and atomic coordinates of NiPtB2-x and Pt2B were refined in the scope of generalized gradient approximation. Chemical bonding analysis by means of the electron localizability approach, supported by Bader charge analysis, reveals a strong electron contribution of Ni atoms for stabilization of the boron zigzag chains, wherein boron atoms are bonded covalently. Bonding within the platinum boride partial structures in the studied compounds varies depending on the atom coordination of boron: from covalent in both the NiPtB2-x structure and trigonal prismatic slabs in Pt2B to mixed metallic with covalent contributions in [BPt6] octahedra in Pt2B. Electrical resistivity measurements characterize NiPtB2-x as a metal with no phase transitions in the temperature range from 2 to 300 K, in concord with electronic band structure calculations and specific heat measurements. The compound is characterized by a positive Hall coefficient at 20 K. This work unveils a new elemental space on realizing novel layered boride structural arrangements and provides a reference for future experiments.

Density functional theory study of Chlorine, Fluorine, Nitrogen, and Sulfur doped rutile TiO2 for photocatalytic application

This study uses the Quantum ESPRESSO code to introduce Hubbard correction (U) to the density functional theory (DFT) in order to examine the effects of non-metals (C, F, N, and S) doping on the structural, electronic, and optical characteristics of rutile TiO2. Rutile TiO2 is a substance that shows promise for use in renewable energy production, including fuels and solar energy, as well as environmental cleanup. Its wide bandgap, however, restricts their uses to areas with UV light. In order to move the rutile TiO2 absorption edge toward visible light, one atom of each dopant was substituted at oxygen atom locations in this work. The calculated band structures yielded a bandgap of 3.03 eV for pure rutile TiO2, which is in good agreement with the experimental measurement. The bandgap of all doped materials, with the exception of F-doped TiO2, displayed a redshift. The absorption edges in C, N, and S-doped TiO2 are displaced toward the visible area, as indicated by the imaginary component of the dielectric function peaks. The appropriateness of C, N, and S-doped TiO2 for photocatalysis applications is demonstrated by the shift in the absorption coefficient to the highest wavelength. The presence of extra charges that attenuate the transmission of light in materials is shown by the increase in refractive index following doping. Furthermore, this discovery is crucial for experimentalists since it helps them understand how non-metal doping affects the characteristics of rutile TiO2 for photocatalysis applications.

Electronic Structure and Optical Properties of GaAs Doped with Rare-Earth Elements (Sc, Y, La, Ce, and Pr)

Herein, the electronic structure and optical properties of GaAs doped with rare-earth elements (Sc, Y, La, Ce, and Pr) were evaluated using the first-principles method. Results showed that the lattice constants and cell volume of GaAs increased after doping. Band structure calculations indicated that the lowest conduction band and highest valence band were evident at the G-point, demonstrating that rare-earth-element doping did not alter the material type of GaAs, which remained a direct-bandgap semiconductor. The bandgap of Sc-doped GaAs increased, whereas those of Y-, La-, Ce-, and Pr-doped GaAs decreased. Moreover, the density of energy levels increased. Doping with Ce and Pr introduced impurity levels, and the Fermi level shifted into the conduction band. Investigation of the optical properties revealed that the static dielectric constant increased with La doping but decreased with Y, La, Ce, and Pr doping. The variation trends of the extinction coefficients of the doped samples were consistent with that of undoped GaAs: the extinction coefficient shifted to a low-energy region. In addition, a slight redshift occurred in the absorption spectrum. The absorption peak also diminished owing to rare-earth-element doping. We concluded that Ce- and Pr-doped GaAs can form metal alloys with different compositions. Such doping may provide a new class of materials for use in optoelectronic devices.

Molecule-Based Proton-Electron Mixed Conductor with the Highest Ambipolar Conductivity.

Proton-electron mixed conductors (PEMCs) are an essential component for potential applications in hydrogen separation and energy conversion devices. However, the exploration of PEMCs with excellent mixed conduction, which is quantified by the ambipolar conductivity, σamb = σeσH/(σe + σH) (σe: electronic conductivity; σH: proton conductivity), is still a great challenge, largely due to the lack of structural characterization of both conducting mechanisms. In this study, we prepared a molecule-based proton-electron mixed-conducting cation radical salt, (ET)4[Pt2(pop)2(Hpop)2]·PhCN (ET: bis(ethylenedithio)tetrathiafulvalene, pop2-: P2H2O52-), by electrocrystallization. The salt shows metallic electronic conduction, which arises from the (ET)2•+ layers, with a high σe value (1-2 S cm-1 at room temperature). The metallic state was corroborated by magnetic susceptibility measurement and band structure calculation. The salt also shows superprotonic conduction (σH = 2.1 × 10-2 S cm-1 at room temperature under dried conditions), which relies on the one-dimensional (1D) hydrogen-bonding network of protonated paddlewheel-type Pt-dimer complex anions, [Pt2(pop)2(Hpop)2]2-. Crystallographic and computational studies revealed the presence of infinite intra- and intermolecular O-H···O hydrogen bonds, which show a double-well-like potential energy curve with a negligible energy barrier in the 1D chain, facilitating Grotthuss-type proton hopping via Lewis basic sites. Among the structurally defined PEMCs, the present salt displays the highest room temperature σamb value of 2.1 × 10-2 S cm-1 even under dried conditions. The σamb value has the same order as those of reported perovskites-type metal oxides at high temperatures and achieves a level that is beneficial for the practical applications.

The tunable electronic band structure of a AlP3/Cs3Bi2I6Cl3 van der Waals heterostructure induced by an electric field: a first-principles study.

Constructing van der Waals heterostructures (vdWHs) has emerged as an attractive strategy to combine and enhance the optoelectronic properties of stacked materials. Herein, by means of first-principles calculations, we investigate the geometric and electronic structures of the AlP3/Cs3Bi2I6Cl3 vdWH as well as its tunable band structure via an external electric field. The AlP3/Cs3Bi2I6Cl3 vdWH is structurally and thermodynamically stable due to the low binding energy and the small energy fluctuation at room temperature. Our band structure calculations demonstrate that the AlP3/Cs3Bi2I6Cl3 vdWH possesses an indirect bandgap and a type-I band alignment with the band edges both dominated by an AlP3 layer. Notably, the band alignment of heterostructures can be flexibly tuned between type-I and type-II by employing an external electric field. Besides, an indirect-to-direct bandgap transition can be observed by increasing the intensity of negative electric field. These results reveal the potential of the AlP3/Cs3Bi2I6Cl3 vdWH as a novel candidate material for the experimental designs of multi-functional devices.

Phase transitions, Dirac and Weyl semimetal states in Mn1−xGexBi2Te4

Using angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT), an experimental and theoretical study of changes in the electronic structure (dispersion dependencies) and corresponding modification of the energy band gap at the Dirac point (DP) for topological insulator (TI) have been carried out with gradual replacement of magnetic Mn atoms by non-magnetic Ge atoms when concentration of the latter was varied from 10% to 75%. It was shown that when Ge concentration increases, the bulk band gap decreases and reaches zero plateau in the concentration range of 45–60% while trivial surface states (TrSS) are present and exhibit an energy splitting of 100 and 70 meV in different types of measurements. It was also shown that TSS disappear from the measured band dispersions at a Ge concentration of about 40%. DFT calculations of band structure were carried out to identify the nature of observed band dispersion features and to analyze the possibility of magnetic Weyl semimetal state formation in this system. These calculations were performed for both antiferromagnetic (AFM) and ferromagnetic (FM) ordering types while the spin-orbit coupling (SOC) strength was varied or a strain (compression or tension) along the c-axis was applied. Calculations show that two different series of topological phase transitions (TPTs) may be implemented in this system, depending on the magnetic ordering. In the case of AFM ordering, the transition between TI and the trivial insulator phase passes through the Dirac semimetal state, whereas for FM phase such route admits three intermediate states instead of one (TI—Dirac semimetal—Weyl semimetal—Dirac semimetal—trivial insulator). Weyl points that form in the FM system along the direction annihilate when either the SOC strength decreases or a sufficient tensile strain is applied, which is accompanied by the corresponding TPTs. Model calculations of the influence of local magnetic ordering in AFM were carried out by alternating Mn layers with Ge-doped layers and showed that the magnetic Weyl semimetal state in this system is reachable at a Ge concentration of approximately 40% without application of any external magnetic fields.

Linkage Regulation of β-Ketoamine Covalent Organic Frameworks for Boosting Photocatalytic Overall Water Splitting.

Two dimensional β-ketoamine covalent organic frameworks (2D TP-COFs) are one category of promising metal-free catalysts for photocatalytic overall water splitting (OWS) because of their unusual stability and versatile electronic/optical properties. However, none of the currently reported TP-COFs can accomplish the hydrogen evolution (HER) and oxygen evolution reactions (OER) simultaneously without adding any sacrificial agents and cocatalysts. To address this challenging issue, we rationally designed 23 2D TP-COFs by regulating the linkage groups and comprehensively evaluated their OWS activity by using the first-principles method. First, the electronic band structure calculations at the HSE06 level reveal that the band gap can be reasonably adjusted with values ranging from 1.67-3.16 eV. Among these 23 systems, 10 TP-COFs are realized to match well with both the chemical potentials of H2/H+ and O2/H2O, which are capable of visible-light-driven OWS from an electronic perspective. Further thermal activity results on OWS demonstrate that only Hep-BDA (heptazine-aniline) and Bpy-4 (bipyrimidinamine) based COFs can satisfy the completely spontaneous of HER and OER under light irradiation and neutral conditions. Importantly, the calculated small exciton binding energies and high carrier mobility for Hep-BDA and Bpy-4 TP-COFs propose they are potentially applied in photocatalytic OWS. We also achieved the theoretical energy conversion efficiency of Hep-BDA can reach as high as 13.01%. Because there are very few successful applications of TP-COFs on OWS, this theoretical work not only offers valuable insights and innovative ideas for the exploration of novel metal-free photocatalysts for OWS but also supplies a direction for the development of new TP-COF derivatives.

Structural, electronic, mechanical, optical and magnetic properties of RhNbZ (Z = Li, Si, As) Half-Heusler compounds: a first-principles study

Abstract Structural, mechanical, electronic, optical and magnetic properties of the cubic RhNbZ (Z = Li, Si, As) half-Heusler compounds is reported using density functional theory (DFT) as implemented in quantum espresso simulation package. Structurally, the compounds are most stable when they are in type I atomic arrangement. Studies of mechanical properties indicate that all the three compounds are ductile in nature and mechanically stable. Calculations of electronic band structure and density of states (DOS) affirm that RhNbSi is a semi-conductor with an indirect band gap of 0.662 eV and 1.0095 eV from generalized gradient approximation (GGA) and GGA+U approaches respectively, where U is Hubbard parameter, RhNbLi has metallic property under both GGA and GGA+U approaches whereas RhNbAs has metallic nature under GGA prediction but it has half-metallic property under GGA+U approach, a property which is essential for spintronic applications. Optical parameters such as dielectric function, reflectivity, refractive index, extinction coefficient, absorption coefficient, optical conductivity and electron energy loss were estimated in the photon energy range of 0–40 eV. Results from these properties calculations reveal that both absorption coefficient and optical conductivity have maximum values whereas electron energy loss has minimum value in the lower energy ranges which show that the materials under our study can be considered as potential candidates for optoelectronic applications. From magnetic property calculations, RhNbSi is predicted to be nonmagnetic material but RhNbLi and RhNbAs have magnetic nature.

TH-graphyne: a new porous bidimensional carbon allotrope.

Graphyne and two-dimensional porous carbon-based materials have garnered significant attention due to their interesting structural characteristics and essential properties for new technological applications. Within this scope, this work investigates the structural, thermal, electronic, optical, and mechanical properties of a novel two-dimensional allotrope that combines triangular (T) and hexagonal (H) rings, connected by acetylenic linkages (graphyne-like), thus named TH-graphyne (TH-GY). This study comprehensively characterizes the proposed system's behavior using density functional theory, ab initio molecular dynamics, and classical reactive molecular dynamics simulations. Our results confirm the structural stability of TH-GY. AIMD simulations demonstrate the material's thermal stability at elevated temperatures, while phonon dispersions indicate its dynamical stability. Electronic band structure calculations show that the system is metallic. The analysis of optical properties reveals intense activity in the visible and UV regions, with pronounced anisotropy. A machine learning interatomic potentials model was developed for TH-GY and used to determine the mechanical behavior of the system, which exhibits Young's modulus ranging from 263 to 356 GPa, highlighting its flexibility. Classical reactive MD simulations elucidate the fracture behavior of TH-GY, revealing distinct fracture patterns and mechanical anisotropy.

Electronic and magnetic properties of GeP monolayer modulated by Ge vacancies and doping with Mn and Fe transition metals.

In this work, Ge vacancies and doping with transition metals (Mn and Fe) are proposed to modulate the electronic and magnetic properties of GeP monolayers. A pristine GeP monolayer is a non-magnetic two-dimensional (2D) material, exhibiting indirect gap semiconductor behavior with an energy gap of 1.34(2.04) eV obtained from PBE(HSE06)-based calculations. Single Ge vacancy (VaGe) and pair Ge vacancies (pVaGe) magnetize the monolayer significantly with total magnetic moments of 2.00 and 2.02 μ B, respectively. Herein, P atoms around the defect sites are the main contributors to the system magnetism. Similarly, the monolayer magnetization is induced by doping with Mn (MnGe) and Fe (FeGe) atoms. In these cases, total magnetic moments of 3.00 and 4.00 μ B are obtained, respectively, and the system magnetism originates mainly from transition metal impurities. The calculated band structures assert the diluted magnetic semiconductor nature of VaGe and FeGe systems, while pVaGe and MnGe systems can be classified as 2D half-metallic materials. Further, the spin orientation in Mn- and Fe-doped GeP monolayers is studied. Results indicate the antiferromagnetic state in the case of doping with pair transition metal atoms. Regardless of the interatomic distance between dopant atoms, Mn-doped systems exhibit ferromagnetic half-metallicity, where the parallel spin orientation is energetically more favorable than the antiparallel configuration. In contrast, the antiparallel spin orientation is stable in Fe-doped systems, which show the antiferromagnetic semiconductor nature. Results presented herein may introduce new prospective 2D spintronic materials made from non-magnetic GeP monolayers.

Antiferromagnetic semiconductor nature in a GeS2 monolayer doped with Mn and Fe transition metals.

The absence of intrinsic magnetism in two-dimensional (2D) materials demands functionalization as necessary for broadening their applications. In this work, doping with transition metals (Mn and Fe) is proposed to modify the electronic and magnetic properties of a GeS2 monolayer. A pristine monolayer is an indirect gap semiconductor with an energy gap of 0.73(1.47) eV computed by using the PBE(HSE06) functional. Significant magnetism with a total magnetic moment of 1.18μB emerges in the GeS2 monolayer upon creating a single Ge vacancy, which is produced mainly by six nearest neighboring S atoms. In this case, the monolayer is metallized with S-px,y states responsible. Similarly, the magnetization of the GeS2 monolayer is also achieved by doping with Mn and Fe atoms with total magnetic moments of 3.00 and 3.78μB, respectively. The calculated band structures imply that the magnetic semiconductor nature with a spin-up/spin-down gap of 0.72/0.53 eV is induced by Mn impurity, while doping with Fe atoms leads to monolayer metallization. Being surrounded by more electronegative S atoms, Mn and Fe impurities lose charge amounts of 1.19 and 1.11e, respectively. Further investigations on spin coupling indicate the antiferromagnetic semiconductor nature in Mn- and Fe-doped systems, regardless of the distance between impurities. Our results provide important insights into the effects of doping into the GeS2 monolayer, which demonstrate that the doped systems hold promise for spintronic applications.

Virtual screening of n-type organic semiconductors using exhaustive band structure calculations

Virtual screening of n-type organic semiconductors using exhaustive band structure calculations

Structural, Electronic, and Magnetic Properties of Ferrimagnetic Double‐Perovskite Ba2GdRuO6: Density Functional Theory and Monte Carlo Simulation

In this study, the structural, electronic, and magnetic properties of the double‐perovskite Ba2GdRuO6 are investigated using both first‐principles calculations and Monte Carlo simulations. Spin–orbit coupling is incorporated to accurately capture the interactions between the 4d and 4f electrons, which play a crucial role in determining the material's magnetic and electronic properties. The calculations showed that the ferrimagnetic structure, with an optimal lattice parameter of 8.41 Å, is the most stable configuration. Additionally, the density of states and band structure calculations reveal a semiconducting nature at the Fermi level, with a total magnetic moment of 4 . To further investigate the system, Monte Carlo simulations are performed to study the effect of crystal fields on the transition temperatures. The results reveal several critical phenomena, including compensation temperature, critical endpoints, and first‐ and second‐order phase transitions.

Full band-structure calculation of semiconducting materials on a noisy quantum processor

Full band-structure calculation of semiconducting materials on a noisy quantum processor

OPTICAL PROPERTIES OF THE AgBiP2Se6 SINGLE CRYSTAL

The AgBiP2Se6 compound has emerged as one of the most studied hexachalcohypodiphosphates in recent years. This is interest is driven by its distinctive layered structure, which implies the possibility of obtaining monolayers and the observation of various of quantum effects. Most studies to date, however, have focused on first-principles calculations, while experimental investigations have primarily been limited to structural analysis and stoichiometric composition determination. This work partially addresses the gap in research by exploring the optical properties of AgBiP2Se6. Transmission spectra within the optical range of 220-1400 nm, as well as Raman spectra, were obtained from single crystalline AgBiP2Se6 samples. The band gap, determined from the transmission spectra using the graphical Tauc method, was found to be 1.44 eV. This value aligns closely with the DFT band-structure calculations using the Perdue-Burke-Erzenhorf (PBE) model without a Hubbard correction parameter (1.384 eV). The Raman spectrum of the AgBiP2Se6 crystal reveals five distinct peaks at approximately 68, 125, 169, 436, and 462 cm-1. The peak at 68 cm-1 can be attributed to the vibrational mode of the cationic centers; the peaks at 125 and 169 cm-1 can correspond to deformations within the Se-P-P and Se-P-Se bonding systems involving changes in bond angles; and the peaks at 436 and 462 cm-1 reflect bond length changes within the anionic (P2Se6)4-group.

A First‐Principles Study of Structural, Elastic, Mechanical, Thermodynamic, and Electronic Properties of Rb2XIO6 (X = Ga, In) Double Perovskites

Double perovskites (DPs) have gained the interest of researchers due to their unique properties. In present work, structural, mechanical, electronic, and thermodynamic properties of Rb2XIO6 (X = Ga, In) DPs are investigated using first‐principles calculations. The tolerance and octahedral factors are calculated in the allowed range of DPs. The phonons dispersion curves were computed with positive frequencies. The elastic constants prove the mechanical stability. Mechanical properties explore the anisotropic, brittle, and stiffer nature of both DPs. The computed band structures discover the metallic nature, where O–p and I–s states are found to cross the Fermi level. Debye temperature for Rb2GaIO6 is calculated higher than Rb2InIO6. Grüneisen parameter is evaluated to decrease with increasing pressure and temperature. Specific heat capacity is observed to saturate at 450 K. The coefficient of thermal expansion are calculated as 9 10−5 and 8.95 10−5 K−1 at 1000 K for Rb2GaIO6 and Rb2InIO6, respectively.

First-principles pressure-dependent investigation of the physical and superconducting properties of ThCr2Si2-type superconductors SrPd2X2 (X = P, As).

The physical and superconducting characteristics of SrPd2P2 and SrPd2As2 compounds with applied pressure were calculated using density functional theory. The pressure effect on the structural properties of these compounds was investigated. The results show that both lattice constants and volume decrease almost linearly with increasing pressure. The elastic constants (C ij) for both compounds increase with increasing pressure and satisfy Born criteria for mechanical stability. The elastic parameters indicate the ductile behaviour and anisotropic nature of these compounds under applied pressure. The Debye temperature (ϴ D) and melting temperature (T m) increase with increasing pressure. The electronic band structure calculation of both compounds exhibits metallic characteristics at different pressures. The density of electronic states at the Fermi level, N(E F), consistently decreases as pressure increases, which is also reflected in the repulsive Coulomb pseudopotential (µ*), and the electron-phonon coupling constant (λ). These optical features suggest that both compounds are suitable for optoelectronic device applications. Furthermore, the superconducting transition temperature, T c, for both compounds is predicted to vary with applied pressure due to changes in ϴ D , N(E F), µ* and λ.

Comparative analysis of electronic and thermoelectric properties of strained and unstrained IrX3 (X = P, As) skutterudite materials

Abstract The electronic and thermoelectric properties of unfilled IrP3 and IrAs3 skutterudites materials under hydrostatic pressures are investigated using density functional theory (DFT) combined with semi-classical Boltzmann transport theory. Calculations of the elastic properties and phonon frequencies for both strained and unstrained materials demonstrate that they are mechanically and dynamically stable, with ductility varying based on the applied pressure. For pressures ranging from 0 to 30 GPa, the band structure calculations with the GGA+TB-mBJ approximation reveal that the band gap varies from 0.400 to 0.144 eV for IrP3 and from 0.341 to 0.515 eV for IrAs3. At 0 GPa, IrAs3 exhibits a direct band gap, whereas IrP3 has an indirect band gap. As pressure increases, IrAs3 undergoes a transition from a direct to an indirect band gap above 10 GPa, while IrP3 maintains its indirect band gap characteristic throughout the pressure range. 
The thermoelectric properties, at various pressures and temperatures between 300 and 1200 K, are also computed. These properties include the Seebeck coefficient, electrical conductivity, thermal conductivity (both electronic and lattice contributions), and relaxation time. The ideal conditions for efficient thermoelectric properties in IrAs3 are achieved at 30 GPa and 1200 K, with an optimal n-type doping concentration of 56×1019 cm-3, resulting in a ZT of 0.68. For IrP3, a ZT of approximately 0.46 is obtained at 600 K and 5 GPa, with a p-type doping concentration of 6.0×1018 cm-3.
The present study provides valuable insights into the behavior of skutterudite materials under strain, offering pathways for enhancing their performance in practical applications.