Electronic Band Structure Properties Research Articles

Electronic Band Structure and Fermi Surface Analysis of Ce2 Ni1-Xcoxge2: A Pseudo Potential Study

This study uses pseudopotential calculations to investigate the electronic band structure and Fermi surface properties of Ce2Ni1-xCoxGe2 alloys. The research problem centers on understanding the effects of Co substitution on the electronic properties of these alloys, particularly regarding potential high-temperature superconducting behavior. The methodology involves density of states (DOS) analysis and Fermi surface calculations for Ce2Ni1-xCoxGe2 alloys with varying Co concentrations. Results reveal a notable increase in DOS around the Fermi level with increasing Co substitution, indicative of enhanced metallic behavior and potential superconducting characteristics. Additionally, band structure analyses demonstrate the significant role of hybridization between Ce 4f, Ni/Co 3d, and Ge 4s/4p orbitals in determining electronic behavior. Fermi surface calculations unveil a transition from near-spherical to complex 2D and 3D shapes with higher Co concentrations, suggesting modifications in Fermi energy surface nestings or electron scattering. This study's conclusions emphasized the intricate electronic structure of Ce2Ni1-xCoxGe2 alloys and highlighted the potential for further exploration in high-temperature super conductivity research.

Detecting Hachimoji DNA: An Eight-Building-Block Genetic System with MoS2 and Janus MoSSe Monolayers.

In the pursuit of personalized medicine, the development of efficient, cost-effective, and reliable DNA sequencing technology is crucial. Nanotechnology, particularly the exploration of two-dimensional materials, has opened different avenues for DNA nucleobase detection, owing to their impressive surface-to-volume ratio. This study employs density functional theory with van der Waals corrections to methodically scrutinize the adsorption behavior and electronic band structure properties of a DNA system composed of eight hachimoji nucleotide letters adsorbed on both MoS2 and MoSSe monolayers. Through a comprehensive conformational search, we pinpoint the most favorable adsorption sites, quantifying their adsorption energies and charge transfer properties. The analysis of electronic band structure unveils the emergence of flat bands in close proximity to the Fermi level post-adsorption, a departure from the pristine MoS2 and MoSSe monolayers. Furthermore, leveraging the nonequilibrium Green's function approach, we compute the current-voltage characteristics, providing valuable insights into the electronic transport properties of the system. All hachimoji bases exhibit physisorption with a horizontal orientation on both monolayers. Notably, base G demonstrates high sensitivity on both substrates. The obtained current-voltage (I-V) characteristics, both without and with base adsorption on MoS2 and the Se side of MoSSe, affirm excellent sensing performance. This research significantly advances our understanding of potential DNA sensing platforms and their electronic characteristics, thereby propelling the endeavor for personalized medicine through enhanced DNA sequencing technologies.

Layer-dependent ultrafast carrier dynamics of PdSe2 investigated by photoemission electron microscopy.

For atomically thin two-dimensional materials, variations in layer thickness can result in significant changes in the electronic energy band structure and physicochemical properties, thereby influencing the carrier dynamics and device performance. In this work, we employ time- and energy-resolved photoemission electron microscopy to reveal the ultrafast carrier dynamics of PdSe2 with different layer thicknesses. We find that for few-layer PdSe2 with a semiconductor phase, an ultrafast hot carrier cooling on a timescale of approximately 0.3 ps and an ultrafast defect trapping on a timescale of approximately 1.3 ps are unveiled, followed by a slower decay of approximately tens of picoseconds. However, for bulk PdSe2 with a semimetal phase, only an ultrafast hot carrier cooling and a slower decay of approximately tens of picoseconds are observed, while the contribution of defect trapping is suppressed with the increase of layer number. Theoretical calculations of the electronic energy band structure further confirm the transition from a semiconductor to a semimetal. Our work demonstrates that TR- and ER-PEEM with ultrahigh spatiotemporal resolution and wide-field imaging capability has great advantages in revealing the intricate details of ultrafast carrier dynamics of nanomaterials.

High carrier mobility ZrSSe/SnX (X=S, Se, S2, Se2) vdW heterostructures for photocatalytic overall water splitting: A first-principles study

Recently, the assembly of novel two-dimensional materials via van der Waals (vdW) interactions to form heterostructures is considered an effective strategy for producing materials with enhanced photocatalytic activities. This study systematically explored the optoelectronic and photocatalytic properties and carrier mobilities of novel ZrSSe/SnX (X = S, Se, S2, Se2) vdW heterostructures using density functional theory. The formation energies, elastic constants, phonon dispersions, and results of ab-initio molecular dynamic simulations indicate structural, mechanical, dynamic, and thermal stability. The electronic band structure and optical properties are calculated using hybrid functional HSE06 for accurate calculations. The results of calculations using the bandgap center technique based on density functional theory show that ZrSSe/SnSe, ZrSSe/SnS2, and ZrSSe/SnSe2 heterostructures possess suitable band edges for photocatalytic overall water splitting. The optical absorption spectrum covers a broad range from 104 in the visible region and increases to 105 in the UV region. Furthermore, the ZrSSe/SnX (X = S, Se, S2, Se2) heterostructures have high carrier mobilities of the order of 105. High mobilities help carriers to move quickly and reduce the recombination rate of holes and electrons. The findings indicate that ZrSSe/SnX (X = S, Se, S2, Se2) heterostructures are potentially efficient visible-light photocatalysts for overall water splitting.

Chemical bonding in lead oxide phosphate Pb10(PO4)6O and in supposed superconductor Pb9Cu(PO4)6O

The electronic band structure and features of the charge density distribution in lead oxide phosphate Pb10(PO4)6O and the copper-doped compound Pb9Cu(PO4)6O have been studied by the density functional theory. Despite the differences in chemical compositions and crystal structures, the type of chemical bonding in the Pb10(PO4)6O and Pb9Cu(PO4)6O compounds was found to be similar to the type of chemical bonding that we previously revealed in high-temperature superconductors and in parent compounds for their production—monoclinic α-Bi2O3 and orthorhombic La2CuO4. Although the lack of experimental data on the electronic band structure and physical properties of the Pb10(PO4)6O and Pb10−xCux(PO4)6O compounds does not currently allow us to conclude that superconductivity could exist at room temperature and atmospheric pressure in the Pb10−xCux(PO4)6O compound, further studies of the properties of lead oxide phosphate and other minerals of the apatite supergroup might be useful for identifying new types of promising materials for the production of high-temperature superconductors.

Electronic band structure and thermoelectric properties of ternary SnSxSe2−x (x = 0,1,2)

In this work, we present a thorough investigation of the electronic structure of layered metal dichalcogenides ternary SnSxSe2−x, where x = 0, 1, and 2. The calculations have been performed by the density functional theory (DFT), density functional perturbation theory (DFPT), and Boltzmann transport theory. It has been found that adding Sulfur to the structure leads to an increase in i) direct and indirect band gaps, ii) the Seebeck coefficient iii) the acoustic and optical branches iv) the power factor v) the lattice thermal conductivity. The thermoelectric properties are studied from the first principle for the whole series of compositions at the highest achievable n- and p-doping levels.

The electronic transport properties of armchair carbon nanotubes with single and multiple horizontal boron-nitride lines: Unusual effects of high bias voltage on I-V characteristics

We investigate the electronic band structure properties for different arrangements of infinite horizontal boron nitride (BN) lines in the (6,6) armchair carbon nanotube. Depending on the arrangement of the boron and nitrogen atoms, the horizontal BN lines can be viewed as single or multiple BN segments along the contour of the host carbon nanotube. According to the geometrical orientation of the BN segment(s) in the circular direction, the band gap energy can be tuned providing semiconducting properties for the parallel geometries and metallic behaviors for the antiparallel geometries respectively. For the non-equilibrium transport properties, the current-voltage characteristics for such structures are also examined. Conventional fluctuations in the current are obtained for the high bias voltage as a sign of the resonant tunneling effects in the electronic transport process. However, unusual current-voltage characteristics are reported for particular BN segment configurations in the anti-parallel multiple geometry. The transmission functions and the local currents are respectively presented pointing out more details about such discrepancy in both the electronic transport process near the Fermi level and the nature of the corresponding wave functions. All calculations are performed by means of the density functional tight-binding approach as implemented in the DFTB+ software package.

Exploring the electronic band structure, spectroscopic signatures, and structural properties of Er3+-based hydroxyapatites co-doped with Ce3+ ions

Exploring the electronic band structure, spectroscopic signatures, and structural properties of Er3+-based hydroxyapatites co-doped with Ce3+ ions

Using orbital sensitivity analysis to pinpoint the role of orbital interactions in thermoelectric power factor

The modification of the electronic band structure is of critical importance for thermoelectric materials whose heat to electricity power generation is related to carrier effective mass and alignment of semiconductor band edges. One approach to optimize the electronic band structure is by modification of orbital interactions through doping or alloying. While the current ab-initio quantum chemical calculations can help us to investigate orbital components of electronic bands, they reveal little information on the relative tunability of electronic states and transport properties with respect to orbital interactions. In this work, we present a method, based on a symmetry-adapted tight-binding model and sensitivity analysis, that can pinpoint the role of orbital interactions in determining electronic band structure and transport properties. As an application, a systematic theoretical analysis is used to show how the power factor of PbTe can/cannot be improved by playing with interatomic orbital interactions. The orbital interaction sensitivity analysis introduced in this work can easily be applied to other compounds or properties.

The charge carrier density modulation in off-stoichiometric ZrNiSn leads to enhanced thermoelectric performance

The off-stoichiometry i.e., ZrNi1+δSn (0<δ<1), and carrier modulation are the two approaches that have separately been found effective mainly to reduce thermal conductivity and improve power factor. This work explores the combined effect of both of these approaches by tuning the carrier density by varying the Sb-concentration in off-stoichiometric ZrNi1.04Sn, which shifts the Fermi level towards the conduction band as confirmed by the band structure calculations. The maximum thermoelectric figure-of-merit ZT∼0.95 at ∼873 K was achieved in the optimum composition ZrNi1.04Sn0.975Sb0.025. For evaluating the device applicability of the synthesized materials, the cumulative temperature dependence (CTD) model was applied, predicting the single leg maximum efficiency ∼8.6% at ΔT ∼ 546 K. A series of calculations have been performed to predict electronic band structure and electronic transport properties to unearth the underlying physics. The microhardness and fracture toughness were determined to ensure that the enhanced thermoelectric performance is not deteriorating mechanical robustness.

Electronic band structure and anisotropic optical properties of bulk and monolayer fullerene networks

We theoretically investigate the local electron density, electronic band structure, density of state, dielectric function, and optical absorption of the bulk and monolayer C60 network structures, based on the latest experimental synthesis [Nature, 2022, 606, 507]. The results show that the ground state electrons are concentrated on the bridge bonds between clusters, the bulk and monolayer C60 network structures have strong absorption peaks in the visible and near infrared regions, and the monolayer quasi-tetragonal phase C60 network structure shows strong polarization dependence. Our results not only provide insights into the physical mechanism of optical absorption of the monolayer C60 network structure, but also reveal potential applications of the C60 network structure in photoelectric devices.

Electronic band structure and optical properties of Li2In2GeSe6 crystal

We present results of a complex experimental and theoretical study of peculiarities of the electronic structure and optical constants of Li2In2GeSe6 compound crystallizing in monoclinic non-centrosymmetric space group Cc. In particular, we have measured the XPS spectra of core-level and valence electrons of atoms composing a high optical quality Li2In2GeSe6 crystal for both pristine and treated with middle-energy Ar+ ions surfaces. Furthermore, the XPS spectrum as measured for the valence-band range of the Li2In2GeSe6 crystal is compared with the total density of states (DOS) theoretically calculated within a density functional theory (DFT) framework as implemented in the augmented plane wave plus local orbitals (APW+lo) method. The present theoretical APW+lo results reveal a very good agreement regarding the shapes and energy positions of main features of the theoretical total DOS curve and the experimental XPS spectrum when the first-principles DFT calculations are made using the modified Becke-Johnson (mBJ) functional in the form of Tran-Blaha and involving the Hubbard correction parameter U treated for highly correlated In 4d electrons (TB-mBJ+U approach). This technique gives also band gap value of 2.26 eV, which is in good agreement with that experimentally measured for this compound. The present TB-mBJ calculations indicate that, at the top and in the upper region of the valence band, Se 4p states make the biggest contributions; the central region is formed mainly by Ge 4p states, while In 5s states dominate at the bottom and in the lower portion of the Li2In2GeSe6 valence band. With respect to peculiarities of filling the valence band by Se(Ge) 4p states, the present calculations are verified experimentally. Furthermore, the optical properties of Li2In2GeSe6 are studied theoretically in detail employing the TB-mBJ+U technique.

Stability, electronic band structure, magnetic, optical and thermoelectric properties of CoXCrZ (X = Fe, Mn and Z = Al, Si) and FeMnCrSb quaternary Heusler

• The stability of these quaternary Heusler alloys has studied from the calculation of their cohesion energy. • The magnetization of these quaternary Heusler comes mainly from the 3d electrons of the Fe, Co, Mn and Cr atoms. In these materials, one spin has a finite density of states at the Fermi level, the other has a band gap. • The electronic structure of Heusler alloys depend on the degree of structural order and distribution of the atoms in the crystal lattice. CoFeCrAl, CoFeMnSi, CoMnCrSi, and FeMnCrSb Heusler alloys show SGS behavior with high Curie temperatures, thus making them suitable substitutes for diluted magnetic semi-conductors. • The increase in temperature for the spin up case reduces the figure of merit and increases the total electronic conductivity in these quaternary Heusler. • The resistivity of studied quaternary alloys is little sensitive to the temperature, while the electronic conductivity and power factor are proportional to the temperature. Ab-initio simulations based on density functional theory as contained in the WIEN2k code using GGA, GGA+U, and mBJ approximations were used to perform the calculations. The energy of cohesion is minimal for FeMnCrSb, indicating that it is the most stable structure, with a lattice constant of 5.95 Å and 6.2184 Å for GGA and GGA+U. The ferromagnetic state is less stable than ferrimagnetic states in all studied quaternary Heusler. All the band structures are metallic, with the exception of the spin up case using GGA+U and mBJ approaches, where the semiconducting character is predicted. The amount of absorption and band gap validate the candidature of CoFeCrAl, CoFeMnSi, CoMnCrSi, and FeMnCrSb as absorber materials for photovoltaic devices. The high values of 0.8, 0.9, 0.95 and 1 for figure of merit (ZT) at 300 K were obtained for CoFeMnSi, CoFeCrAl, CoMnCrSi, and FeMnCrSb allowing their use in spintronic and thermoelectric applications. The resistivity of studied quaternary alloys is little sensitive to the temperature, while the electronic conductivity and power factor are proportional to the temperature. Ferromagnetic (Ferro) and possible ferrimagnetic (Ferri) configurations of quaternary Heusler XX'YZ.

First-principles calculations to investigate electronic band structure, optical and mechanical properties of new CaFCl monolayer

Two-dimensional materials present new opportunities to venture into largely unexplored areas of material property space. They are appropriate for several electronic powers, photonics, and sunlight device applications. In this framework, leveraging density functional theory and even beyond, we investigate the structural, vibrational, electronic, optical, and elastic properties of novel CaFCl thin film. We have found that the CaFCl sheet is dynamically stable because its spectrum contains no imaginary frequencies. The direct band gap energy value of our GW findings is around 9.10 eV, which really is higher than the band gaps of ScOI and InOF oxyhalides thin films. We have found that the external electric fields immediately affect the structure of the layer. The band gap of the CaFCl structure is reduced rapidly by increasing the strength of the electric field. Additionally, our Bethe–Salpeter theory calculations demonstrate that when the excitation light rate is greater than the resonance frequency (8.00 eV), the substance becomes translucent. We have also used the method of homogeneous deformation, which is coupled with density functional theory and random phase approximation total-energy computations to produce a comprehensive scheme for studying the second-and third-order elastic constants for the CaFCl layer. A polynomial fit to the estimated energy-strain connection yielded these constants. Our results reveal that this 2D monolayer is a promising material for nanophotonics and optoelectronics.

Theoretical prediction by DFT on properties of β′-SrTa2O6 crystal

Based on the Density Functional Theory (DFT) electronic band structure, state density, linear optics, elastic, dynamic and thermodynamic properties of ??-SrTa2O6 crystal with P4/mbm (No. 127) space group were investigated with the help of ABINIT and Wien2k code. In the study, it was found that the ??-SrTa2O6 crystal is classified as a semiconductor with an indirect bandgap. For this crystal, the dielectric function was obtained and optical constants such as energy loss function, extinction coefficient, absorption coefficient and reflectivity were calculated. The components of the elastic stiffness tensor, the phonon dispersion, the state density and the contribution of each atom to the state density were obtained. Finally, thermodynamic properties were determined for the ??-SrTa2O6 crystal. Furthermore, the changes in free energy (F), internal energy (E), entropy (S) and heat capacity (C) depending on the temperature were investigated.

First-principles study of BX-SiS (X = As, P) van der Waals heterostructures for enhanced photocatalytic performance.

The vertical integration of two-dimensional (2D) materials through weak van der Waals (vdW) interactions is gaining tremendous attention for application in nanotechnology and photovoltaics. Here, we performed first-principles study of the electronic band structure, optical and photocatalytic properties of vertically stacked heterostructures based on boron pnictides BX (X = As, P) and SiS monolayers. Both heterobilayers possess a stable geometry and reveal type I band alignment with a direct band gap, indicating substantial transfer of charge across the junction of the same layer. Interestingly, a redshift is found in the visible light region of the optical absorption spectra of BX-SiS heterobilayers. The comparatively larger hole mobility (14 000 cm2 V-1 s-1) of BP-SiS preferably allows hole conduction in the zigzag-direction. More importantly, the excellent band edge values of the standard redox potential and smaller Gibbs free energy for the adsorption of hydrogen (ΔGH*) make them ideal for performing the hydrogen evolution reaction (HER) mechanism under solar irradiation. These findings offer exciting opportunities for developing next-generation devices based on BX-SiS heterobilayers for promising applications in nanoelectronics, optoelectronic devices and photocatalysts for water dissociation into hydrogen to produce renewable clean energy.

WanTiBEXOS: A Wannier based Tight Binding code for electronic band structure, excitonic and optoelectronic properties of solids

The Bethe–Salpeter equation (BSE) approach becomes a methodology commonly used for simulating excitonic and optical properties in computer materials sciences. However, BSE approach based directly on first principles demands a high computational cost, being prohibitive for larger systems. In order to overcome this challenge, we have developed WanTiBEXOS, a parallel computational FORTRAN code, constituted of a maximally localized Wannier functions based tight-binding (MLWF-TB) model in conjunction with BSE framework. The MLWF-TB Hamiltonian used in WanTiBEXOS package can be obtained via any density functional theory package interfaced with Wannier90 code. It's expected, due MLWF-TB formalism, a computational time reduction around one or more orders of magnitude in comparison with BSE ab initio implementations. In order to demonstrate its reliability, flexibility, efficiency and versatility of WanTiBEXOS, we simulate electronic and optical property calculations for the representative materials, including conventional bulk semiconductors, perovskites, nano-monolayer materials and van der Waals heterostructures. Program summaryProgram Title: WanTiBEXOSCPC Library link to program files:https://doi.org/10.17632/4vh76mnkv5.1Developer's repository link:https://github.com/ac-dias/wantibexosLicensing provisions: GNU General Public Licence 3.0Programming language: Fortran90 (Intel compiler)External routines: OpenMP and Intel Math Kernel Library (MKL)Nature of problem: Calculate electronic, optical, and excitonic properties of solids.Solution method: Tight-binding approach under maximally localized Wannier functions (MLWF) parametrization to describe standard electronic properties and the Bethe–Salpeter formalism for excitonic properties.

A novel optical temperature sensor based on Boltzmann function in BiZn2PO6 phosphor

In this paper, a new scheme of optical temperature measurement based on Boltzmann function is reported for the first time. The BiZn2PO6 and BiZn2PO6:Eu3+ phosphors with strong host emission intensity were investigated from the perspective of crystal structure, electronic band structure, phonon distribution, and fluorescence properties. By exploring the relationship between host emission intensity and temperature, or between fluorescence lifetime and temperature, a novel optical temperature sensor based on Boltzmann function was designed. With this scheme, the performance of the optical temperature sensors can be visualized in the fitting results of Boltzmann function. The absolute sensitivity of the optical temperature sensor designed based on this function reaches a maximum value Sa=14dT at T0, while relative sensitivity is 12dT. For example, in BiZn2PO6 phosphor, the absolute and relative sensitivities reached 0.88% and 1.78% at 260 K. Therefore, the new optical temperature sensor based on Boltzmann function provides the theoretical basis and practical experience for the development of high-sensitivity non-contact optical temperature sensor.

A study of anisotropic thermoelectric properties of bulk Germanium Sulfide in its Pnma phase: a combined first-principles and machine-learning approach

This work reports a detailed and systematic theoretical study of the anisotropic thermoelectric properties of bulk Germanium Sulfide (GeS) in its orthorhombic Pnma phase. Density functional theory (DFT), employing the generalized gradient approximation (GGA), has been used to examine the structural and electronic band structure properties of bulk GeS. Electronic transport properties have been studied by solving semiclassical Boltzmann transport equations. A machine-learning approach has been used to estimate the temperature-dependent lattice part of thermal conductivity. The study reveals that GeS has a direct band gap of 1.20 eV. Lattice thermal conductivity is lowest along crystallographic a-direction, with a minimum of ∼0.98 Wm −1 K −1 at 700 K. We have obtained the maximum figure of merit (ZT) ∼ 0.73 at 700 K and the efficiency ∼7.86% in a working temperature range of 300 K–700 K for pristine GeS along crystallographic a-direction.

Photoinduced band renormalization effects in the topological nodal-line semimetal ZrSiS

Out-of-equilibrium effects provide an elegant pathway for probing and understanding the underlying physics of topological materials. In particular, controlling electronic band structure properties using ultrafast optical pulses has shown promise for creating exotic states of matter. Of recent interest is band renormalization in Dirac and Weyl semimetals as it leads to direct physical observables through the enhancement of the effective mass or in the shift of resonant energies. Here we provide experimental and theoretical signatures of photoinduced renormalization of the electronic band structure in the topological nodal-line semimetal ZrSiS. Specifically, we show how the change in the transient reflectivity spectra under femtosecond optical excitations is induced by out-of-equilibrium effects that renormalize the kinetic energy of electrons. We associate the observed spectral features with an enhancement of the effective mass and to a redshift of the resonant frequency as a function of pump field strength. Finally, we show that the transient relaxation dynamics of the reflectivity is primarily an electronic effect with a negligible phononic contribution. Our study presents conclusive modifications of electronic properties in ZrSiS using ultrashort pulses and demonstrates the potential of this approach in creating photoinduced phases in topological quantum matter through an all-optical route.