Resulting Band Structure Research Articles

Impact of halogens modifications on physical characteristics of lead-free hybrid double perovskites compounds Cs2YCuX6 (X=Cl, Br, and I) for energy storage applications: First principles investigations

The purpose of this study is to examine the structural, electronic, optical, and thermoelectric features of novel double perovskite Cs2YCuX6 (X=Cl, Br, and I) for the first time in order to look for potential applications in solar power systems. Using first-principles calculations based on the widely recognized Density Functional Theory (DFT) and the PBE-Generalized Gradient Approximation (GGA) functional included in the WEIN2k package, the characteristics of the perovskites were determined. From the results of band structure and Total Density of States (TDOS) the energy band gap of Cs2YCuCl6, Cs2YCuBr6, and Cs2YCuI6 are observed 2.34 eV, 2.03 eV and 1.68 eV respectively. The PDOS outcomes shows that the formation of the valance and conduction bands is due to the hybridization of Cu-3d and halogen ions such that (X=Cl, Br, and I). The calculated values of goldsmith’s tolerance factor and formation energy reveal that the examined halide perovskites are structurally and thermodynamically stable. The electron localization function ELF and bader charge analysis show that the ionic nature between Cs and halogen ions X. Regarding the optical behavior, Cs2YCuI6has shown maximum absorption of electromagnetic radiation and conductivity in the ultraviolet and visible region i.e. (128–471 nm) which makes it a suitable candidate for optoelectronic and solar cell applications. The thermoelectric properties of the studied compounds have been calculated by means of the Boltztrap code. The presented findings unveil that amongst all studied compoundsCs2YCuI6 is best candidate for solar cell and thermoelectric applications due to higher conductivity, larger absorption range, significant Seebeck coefficient and higher Power factor.

Generalized Bloch Theorem and Band-Structure Topology

Dispersion relations in a metal with a commensurate helical magnetic order are considered in the framework of one- and two-dimensional tight-binding models. The generalized Bloch theorem for translations combined with spin rotations, together with the Born–Karman periodic boundary conditions, leads to the appearance of multisheet dispersion curves (surfaces). It is demonstrated that the resulting band structure is topologically nontrivial, which can lead to a spin textured Fermi surface and cause transport anomalies.

Computational investigation of electronic, thermoelectric, and optical properties in Cs2Li[formula omitted](X = Br, I) for energy harvesting applications

The remarkable potential of double perovskite materials, characterized by lead-free, non-toxic attributes and robust dynamical stability, positions them as highly promising candidates for both thermoelectric and optoelectronic applications. In light of this, a comprehensive investigation is undertaken through density functional theory to thoroughly explore the optoelectronic and transport characteristics of Cs2LiBiX6 (X = Br, I) double perovskite materials. To ascertain dynamic stability, phonon dispersion band structures are computed, and the structural stability is evaluated through the tolerance factor. The resulting band structures reveal narrow band gaps of 3.45 eV and 1.79 eV for the Br and Indium-based DPs, respectively. These narrow band gaps hold significant importance for applications such as ultraviolet detectors and other optoelectronic devices that function in the visible and UV-light spectrum. Notably, absorption peaks of maximal intensity emerge at 5.1 eV (76 nm) and 4.0 eV (67 nm) for the Br and Indium-based double perovskites, respectively. Furthermore, a comprehensive analysis of thermoelectric behavior is conducted, encompassing the figure of merit, power factor, Seebeck coefficient, and the ratio of electrical to thermal conductivity across a temperature range of 50–800 K. The exceptionally low lattice vibration values, coupled with a substantial enhancement in the thermoelectric figure of merit (ZT), notably underscore their significance for advanced thermoelectric generator applications.

The first principle study on the hydrogen storage properties of monolayer and bilayer α-graphyne decorated by alkali metal atoms

Using the first-principles density functional theory, the hydrogen storage properties of monolayer and bilayer α-graphyne systems decorated by alkali metal are investigated. The results of band structure and density of state analysis indicate that alkali metal decoration enhances the chemical activity of the adsorption substrate, leading to increased H2 adsorption capacities for Li, Na and K decorated monolayer systems (15.0 wt.%, 14.5 wt.%, 10.7 wt.%, respectively). The combined action of interlayer force and decorated metal atoms results in higher H2 adsorption capacities for Li, Na and K decorated bilayer systems (17.7 wt.%, 16.9 wt.%, 13.0 wt.%, respectively), which means the bilayer graphyne structures enhance the storage capacities for decorated structures. Additionally, the Na decorated rhombus bilayer system demonstrates the highest adsorption density of H2 molecules between α-graphyne layers. Overall, alkali metal decorated monolayer and bilayer systems exhibit promising H2 adsorption potentials.

Electric field and strain tuned the electronic and optical properties of Zr2CO2/MoSe2 van der Waals heterojunction

Two-dimensional semiconductor materials have attracted significant research interest due to their exceptional properties in various applications. Among them, transition-metal dichalcogenides and MXenes have emerged as widely used materials in photoelectronic devices due to their excellent optical and electronic properties. In this study, we investigate the electronic and optical properties of MXene/MX2 heterojunctions by employing First Principles based on density functional theory calculations on Zr2CO2/MoSe2 van der Waals heterojunctions. The results of band structure, density of states and band alignment demonstrate that the Zr2CO2/MoSe2 heterojunction is a type-II band alignment with an indirect bandgap of 0.93 eV. We further explore the impact of electric fields and strains on their electronic and optical performance. The results show that carriers can be effectively separated for designing high-performance devices in photocatalysis under electric fields ranging from −0.5 to 0.5 V/Å and biaxial strains ranging from −4% to 10 %. The formation of the Zr2CO2/MoSe2 heterojunction allows for enhanced coefficient and a broader light absorption range compared to the individual Zr2CO2 and MoSe2 components. In consequence, this study contributes to a fundamental understanding of Zr2CO2/MoSe2 heterojunctions and their potential applications in photocatalysis.

Introduction of Local Resonators to a Nonlinear Metamaterial With Topological Features

Abstract Recent work in nonlinear topological metamaterials has revealed many useful properties such as amplitude dependent localized vibration modes and nonreciprocal wave propagation. However, thus far, there have not been any studies to include the use of local resonators in these systems. This work seeks to fill that gap through investigating a nonlinear quasi-periodic metamaterial with periodic local resonator attachments. We model a one-dimensional metamaterial lattice as a spring-mass chain with coupled local resonators. Quasi-periodic modulation in the nonlinear connecting springs is utilized to achieve topological features. For comparison, a similar system without local resonators is also modeled. Both analytical and numerical methods are used to study this system. The dispersion relation of the infinite chain of the proposed system is determined analytically through the perturbation method of multiple scales. This analytical solution is compared to the finite chain response, estimated using the method of harmonic balance and solved numerically. The resulting band structures and mode shapes are used to study the effects of quasi-periodic parameters and excitation amplitude on the system behavior both with and without the presence of local resonators. Specifically, the impact of local resonators on topological features such as edge modes is established, demonstrating the appearance of a trivial bandgap and multiple localized edge states for both main cells and local resonators. These results highlight the interplay between local resonance and nonlinearity in a topological metamaterial demonstrating for the first time the presence of an amplitude invariant bandgap alongside amplitude dependent topological bandgaps.

Optoelectronic and mechanical properties of gallium arsenide alloys: Based on density functional theory

First principles calculations based on density functional theory (DFT) were performed to investigate the structural, electronic, optical and mechanical properties of pristine GaAs compound and its alloy; Ga0.75Al0.25As, Ga0.75In0.25As, Ga0.75Sn0.25As, Ga0.75Ti0.25As. WIEN2K and Quantum expresso (QE) codes were adopted for calculations using generalized gradient approximation (GGA) in Perdew-Burke Erzenhoff (PBE) as exchange correlation function for both codes. Full potential linear augmented plane wave (FPLAPW) with the local orbital method was adopted as implement in WIEN2K code. In QE code, norm-conserving pseudopotentials were employed on a plane-wave expansion of the wave functions. Structural and electronic properties were elaborated since their result gives information about the optical and mechanical performance. Electronic band structure and optical parameters were performed using WIEN2K code. Underestimation of band gap observed from DFT calculations were corrected by using Modified Becke and Johnson (mBJ). Mechanical components were determined using QE with thermo_pw package. Lattice constant, volume, bulk modulus and other physical parameters were calculated for structural properties. Discrepancy in these parameters as observed in crystal structure is associated to difference in ionic radius of host and substituted atom. The results of band structure and density of states were calculated for electronic properties. All the studied compounds were semiconductors in nature except Ga0.75Sn0.25As which displayed metallic character. Optical parameters including extinction coefficient, absorption coefficient, refractive index, optical conductivity, optical reflectivity and energy loss function have been computed from the dielectric function at energy range of 0 to 25 eV using the Kramers-Kronig transformations. Calculated elastic function were used to compute the mechanical properties such as anisotropic, brittle characteristics, stiffness and many others. All the results were compared with available theoretical and experimental records.

Resonant Band Hybridization in Alloyed Transition Metal Dichalcogenide Heterobilayers.

Bandstructure engineering using alloying is widely utilized for achieving optimized performance in modern semiconductor devices. While alloying has been studied in monolayer transition metal dichalcogenides, its application in van der Waals heterostructures built from atomically thin layers is largely unexplored. Here, heterobilayers made from monolayers of WSe2 (or MoSe2) and MoxW1 - xSe2 alloy are fabricated and nontrivial tuning of the resultant bandstructure is observed as a function of concentration x. This evolution is monitored by measuring the energy of photoluminescence (PL) of the interlayer exciton (IX) composed of an electron and hole residing in different monolayers. In MoxW1 - xSe2/WSe2, a strong IX energy shift of ≈100 meV is observed for x varied from 1 to 0.6. However, for x < 0.6 this shift saturates and the IX PL energy asymptotically approaches that of the indirect bandgap in bilayer WSe2. This observation is theoretically interpreted as the strong variation of the conduction band K valley for x > 0.6, with IX PL arising from the K - K transition, while for x < 0.6, the bandstructure hybridization becomes prevalent leading to the dominating momentum-indirect K - Q transition. This bandstructure hybridization is accompanied with strong modification of IX PL dynamics and nonlinear exciton properties. This work provides foundation for bandstructure engineering in van der Waals heterostructures highlighting the importance of hybridization effects and opening a way to devices with accurately tailored electronicproperties.

Exploring the multifaceted properties: electronic, magnetic, Curie temperature, elastic, thermal, and thermoelectric characteristics of gadolinium-filled PtSb3 skutterudite.

The investigation of binary and filled skutterudite structures, particularly PtSb3 and GdPt4Sb12, has gained significant attention, becoming a focal point in scientific research. This comprehensive report delves into the intrinsic characteristics of these structures using Density Functional Theory (DFT). Initially, we assess the structural stability of PtSb3 and GdPt4Sb12 by examining their total ground state energy and cohesive energy, employing the Brich Murnaghan equation of state to determine stability in various configurations. Further insights are gained by exploring second-order elastic constants (SOEC's) to extend our understanding of structural stability. The electronic structures are then meticulously defined through a quantum mechanical treatment, employing a combination of two distinct spin-polarized approximation schemes: Perdew-Burke-Ernzerhof Generalised Gradient Approximation (PBE-GGA) and Tran-Blaha modified Becke-Johnson (TB-mBJ). The resulting band structures reveal a symmetry in electronic behavior, showcasing spin-magnetic moments of 3 μB and 7.58 μB per formula unit, with the primary contributions emanating from the Pt 3d and Pt4+ 3d-transition elements. To gauge thermal stability, we evaluate the phonon-dependent Grüneisen parameter (γ) across specific temperature ranges. The study extends to exploring transport properties as a function of chemical potential (μ - EF) at various temperatures. The findings suggest that these designed materials hold substantial potential for diverse applications, particularly in conventional spin-based and thermoelectric technologies. The comprehensive insights obtained through this investigation pave the way for a deeper understanding and broader implications in various technological domains.

Precise design of TiO2 photocatalyst for efficient photocatalytic H2 production from seawater splitting

The side reactions in seawater and the sedimentation of the photocatalyst in highly concentrated ionic solutions seriously affect the activity and stability of the photocatalyst to split seawater to produce hydrogen. In terms of these problems, we designed the super-hydrophilic mesoporous brookite/anatase TiO2 photocatalyst accordingly. The characterization results of crystal phase and band structure confirmed that the transition from brookite/rutile type I hetero-phase junction to brookite/anatase type II hetero-phase junction. Without any sacrificial agents, the photocatalytic H2 production rate from seawater splitting reached 6.59 mmol g−1 h−1, which was 2.5 times and 2.9 times higher than brookite/rutile TiO2 and anatase/rutile TiO2 (P25), respectively. Meanwhile, it was also 4.4 times, 11.8 times and 36.1 times higher than brookite, anatase and rutile nanoparticles. Furthermore, the contact angle test confirmed the superhydrophilicity of the photocatalyst, mitigating the side reactions induced by Cl− and ensuring the long-term stability (100 h) of the photocatalyst in seawater.

A method of calculating bandstructure in real-space with application to all-electron and full potential

We introduce a practical and efficient approach for calculating the all-electron full potential bandstructure in real space, employing a finite element basis. As an alternative to the k-space method, the method involves the self-consistent solution of the Kohn-Sham equation within a larger finite system that encloses the unit-cell. It is based on the fact that the net potential of the unit-cell converges at a certain radius point. Bandstructure results are then obtained by performing non-self-consistent calculations in the Brillouin zone. Numerous numerical experiments demonstrate that the obtained valence and conduction bands are in excellent agreement with the pseudopotential k-space method. Moreover, we successfully observe the band bending of core electrons.

Theoretical simulation of optoelectronic and structural properties of ASiN2 (A = Be, Mg, Ca, Sr) semiconductors

Using first-principles calculations, we have explored the structural, electronic and optical properties of ternary chalcopyrites ASiN2 (A = Be, Mg, Ca, Sr). The calculations were performed with the modified Becke-Johnson (mBJ) exchange potential, shows that the ASiN2 (A = Be, Mg) compounds have a direct band gap while CaSiN2 and SrSiN2 have an indirect gap. We present the results of band structure and density of states, which predicts that the energy band gap of these compounds decreases when we migrate from Be to Sr. The electron charge density plots understood the interlayer and chemical bonding properties, which also revealed the materials' unique traits with regard to their optical properties. The dielectric function, absorption coefficient, refractive index, and optical conductivity have all shown significant changes. The calculated optical results show that these materials are promising semiconductors for photovoltaic applications.

Novel chair graphene nanotubes as adsorbing medium for alanine and asparagine amino acids – A DFT outlook

Amino acids are required to make protein. The deficiency of amino acids leads to a lack of sleep and mood. Among various amino acids, we conducted the adsorption studies of alanine and asparagine amino acids on a novel one-dimensional material, chair graphene nanotube. The stability of the chair graphene nanotube is ensured with the negative formation energy, which is −6.490 eV/atom. The energy band gap of bare chair graphene nanotube is 1.022 eV, which possesses a semiconductor nature. The stable chair graphene nanotube is used as adsorbing material for alanine and asparagine amino acids. Besides, alanine and asparagine are physisorbed on chair graphene nanotubes that are confirmed by the range of adsorption energy from −0.107 eV to −0.718 eV. Upon adsorption of amino acids, the charge transfer outcome shows that chair graphene nanotubes behave as donors of electrons to alanine and asparagine. Further, the changes in the band gap of the chair graphene nanotube are noticed from the results of band structure and PDOS spectrum. The changes in the electron density also reveal the changes in the electronic properties of the chair graphene nanotube owing to alanine and asparagine sorption. The proposed report portrays the adsorption attributes of alanine and asparagine amino acids on 1D chair graphene nanotubes.

First-Principles Insights into Structural, Optoelectronic, and Elastic Properties of Fluoro-Perovskites KXF3 (X = Ru, Os).

The need for new and better semiconductor materials for use in renewable energy devices motivates us to study KRuF3 and KOsF3 fluoride materials. In the present work, we computationally studied these materials and elaborate their varied properties comprehensively with the assistance of density functional theory-based techniques. To find the structural stability of these under-consideration materials, we employed the Birch-Murnaghan fit, while their electronic characteristics were determined with the usage of modified potential of Becke-Johnson. During the study, it became evident from the band-structure results of the KRuF3 and KOsF3 materials that both present an indirect semiconductor nature having the band gap values of 2.1 and 1.7 eV, respectively. For both the studied materials, the three essential elastic constants were determined first, which were further used to evaluate all the mechanical parameters of the studied materials. From the calculated values of Pugh's ratio and Poisson's ratio for the KRuF3 and KOsF3 materials, both were verified to procure the nature of ductility. During the study, we concluded from the results of absorption coefficient and optical conduction in the UV energy range that both the studied materials proved their ability for utilization in the numerous future optoelectronic devices.

WS2 and WSSe bilayer with excellent carrier mobility and power conversion efficiency

The WS2/WSSe and WSSe/WS2 bilayers are constructed using single-layer WS2 and WSSe with a lattice mismatch rate of only 1.85 %, and their structural properties, carrier mobility, electrical properties, and photocatalytic performance are performed using density functional theory. The carrier mobility of WS2/WSSe and WSSe/WS2 bilayers is better than that of single-layer WS2. And the conductivity of the WSSe/WS2 bilayer in the Zigzag direction is superior to that in the Armchair direction. The results of band structure using the HSE06 method demonstrate that the most stable WS2/WSSe and WSSe/WS2 bilayers are type-II band alignment. WS2/WSSe and WSSe/WS2 bilayers can undergo redox reactions at pH = 0 and pH = 7 respectively. And they all emerge a built-in electric field to cause photo-generated carriers to recombine between the layers to upgrade the photocatalytic performance of the bilayer, which is a typical S-scheme heterojunction. And the power conversion efficiency (PCE) of the WS2/WSSe and WSSe/WS2 bilayers are 15.5 % and 15.7 % respectively, so the utilization rate of sunlight is relatively high. In general, WS2/WSSe and WSSe/WS2 bilayers are ideal materials in the field of photocatalytic water splitting.

Surface Electronic Structure Engineering of Manganese Bismuth Tellurides Guided by Micro-Focused Angle-Resolved Photoemission.

Modification of the electronic structure of quantum matter by ad atom deposition allows for directed fundamental design of electronic and magnetic properties. This concept is utilized in the present study in order to tune the surface electronic structure of magnetic topological insulators based on MnBi2 Te4 . The topological bands of these systems are typically strongly electron-doped and hybridized with a manifold of surface states that place the salient topological states out of reach of electron transport and practical applications. In this study, micro-focused angle-resolved photoemission spectroscopy (microARPES) provides direct access to the termination-dependent dispersion of MnBi2 Te4 and MnBi4 Te7 during in situ deposition of rubidium atoms. The resulting band structure changes are found to be highly complex, encompassing coverage-dependent ambipolar doping effects, removal of surface state hybridization, and the collapse of a surface state band gap. In addition, doping-dependent band bending is found to give rise to tunable quantum well states. This wide range of observed electronic structure modifications can provide new ways to exploit the topological states and the rich surface electronic structures of manganese bismuthtellurides.

Bending deformation regulates the electronic structure and optical properties of Na adsorbed borophene

In the present paper, the effect of different bent angles on structural stability, electronic structure, and optical properties of Na absorbed borophene system is investigated using the density functional theory. The structure of the borophene was almost unchanged and the planar structure was not disrupted after the adsorption of a Na atom. Directly above the bottom B–B bonds is considered as the optimal adsorption position of single. The stability of the Na adsorbed borophene system can be decreased under the condition of different bent angles. The adsorption of Na atoms changes the energy band structure of the intrinsic borophene according to the calculation results of energy band structure and density of states, which resulting the conduction band contains more impurities. The 2p orbital of Na and the 3p orbital of B hybridize between −4 eV and 6 eV. Bending deformation gives rise to the electron transfer between Na atoms and B atoms. In terms of optical properties, the bending deformation improves the absorption of infrared light and the catalytic activity of light in the adsorbed system.

Elastic, piezoelectric, and electronic properties of K1−xMxNbO3 (M = Li, Na): A first-principles study

The structural, elastic, piezoelectric, and electronic properties of K1−xMxNbO3 (M = Li, Na) were investigated by first-principles calculations. The results show that the modifications have effects on the elastic properties of KNbO3 and strengthen the anisotropy. Na and Li doping can slightly improve the piezoelectric stress tensor (e33) and piezoelectric strain tensor (d33) of KNbO3. With the increase in the x value from 0 to 0.5 in K1−xMxNbO3, the d33 value is improved from 24.4 to 36.3 pC/N (M = Na) and 41.5 pC/N (M = Li), and the piezoelectric property is improved by 1.49 and 1.70 times with the modifications of Na and Li, respectively. This conclusion is consistent with the result of Born effective charge and band structure results. The Born effective charge average values (Z*̄) for K and Nb atoms in K0.5M0.5NbO3 (M = Li, Na) are slightly increased compared to those in KNbO3. KNbO3 has an indirect bandgap, while Na and Li doping makes K0.5Na0.5NbO3 or K0.5Li0.5NbO3 a direct bandgap semiconductor. This study may provide a theoretical insight into Na and Li modified KNbO3 for their piezoelectricity.

First principles study of the structural, mechanical and optical properties of argyrodite-structured Ag6PS5X (X= Br, I) compounds

Argyrodite-structured sulphides solid electrolytes, which are currently the most widely utilized solid electrolytes for all-solid-state battery manufacturing have gained reasonable interest recently. Here, the electronic structure, optical and elastic properties of Ag6PS5X (X = Br, I) Silver based Argyrodite have been obtained using density functional theory (DFT). The well-known Perdew-Burke-Ernzerhoff generalized gradient approximation (PBEsol-GGA) was used for calculations of structural and elastic parameters, whereas Tran-Blaha approach of the modified Becke–Johnson (TB-mBJ) potential was used to get more reliable results for the energy band structure of Ag6PS5Br and Ag6PS5I. All these compounds possess cubic structure with lattice constants increasing from 10.71 Å to 10.74 Å for Ag6PS5Br and Ag6PS5I due to increase in atomic number. TB-mBJ functional shows semiconductor nature with direct band gap lying at the gamma symmetry points. The optical conductivity and absorption co-efficient shows their peaks in ultraviolet region by inserting large size anion moving towards a lower energy range. The band gap of these compounds (1.97 eV, 1.88 eV) indicates their potential in single and multi-junction solar cells. The elastic constants clearly show mechanical stability of the compounds. The calculated B/G ratio shows the ductile nature of these compounds while Poisson ratio varies from 0.20 (Br) to 0.26 (I) shows high ionic contribution in intra-atomic bonding.

Tunable magnetic anisotropy, half-metallicity and tunneling magnetoresistance effect of 2D CrI3 in CrI3/MnGeX3 (X = Se, Te) heterostructures under normal compressive strain

The induction of half-metallicity and tunable magnetic anisotropy of CrI3 monolayers remains challenging and unstable. In this study, we demonstrate that half-metallic CrI3 can be induced in a CrI3/MnGeX3(X = Se, Te) heterostructure. Normal compressive (NC) strain can effectively control the half-metallic band gap and spin-polarized electronic transport of CrI3 in CrI3/MnGeSe3. At 6% strain, the half-metallic band gap and equilibrium tunneling magneto-resistance (TMR) increases by 25% and 220%. The results of band structure, force theorem, charge density and work function calculations show that CrI3 in CrI3/MnGeSe3 loses electrons to form a hole-conducting half-metal with in-plane easy magnetization axis, while CrI3 gains electrons in CrI3/MnGeTe3 to form an electron-conducting half-metal with out-of-plane easy magnetization axis. Heterointerfacial half-metallicity in CrI3 is intrinsic without any external physical modification, and the NC strain of a two-dimensional structure can easily be realized experimentally, paving the way for further research of spintronic devices.