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Electronic structure of CuWO<sub>4</sub>: dielectric-dependent, self-consistent hybrid functional study of a Mott-Hubbard type insulator
摘要： Copper tungstate, CuWO4, is a semiconducting oxide with interesting applications in photocatalysis. In this paper we present an accurate study of the electronic properties of stoichiometric and oxygen deficient CuWO4 based on a dielectric dependent hybrid density functional. In CuWO4 the Cu ions (Cu2+) are in a 3d9 configuration, so that the material must be classified as a magnetic insulator. Various magnetic configurations of CuWO4 have been considered, the most stable one being anti-ferromagnetic. The band structure, described in terms of density of states, exhibit the presence of a wide band dominated by W 5d states, separated by about 5 eV from the top of the valence band, consisting of O 2p states partly mixed with Cu 3d states. The empty component of the Cu 3d orbitals forms a narrow band 3.6 eV above the valence band maximum. The electronic structure emerging from the DOS curves and the Kohn-Sham energies is hard to reconcile with an experimental band gap of 2.1-2.3 eV. This gap can be rationalized within the Mott-Hubbard model of magnetic insulators, and has been computed from the total energies of the system with one electron removed from the O 2p band and one electron added to the Cu 3d states. Computing the charge transition levels for CuWO4, we come to a theoretical band gap of 2.1 eV, in excellent agreement with the experimental observations. We also studied the nature of the oxygen vacancy in CuWO4 with particular attention to the electron redistribution following the oxygen removal. The excess electrons, in fact, can occupy the localized 3d states of Cu or the localized 5d states of W. The resulting solution depends on various factors, including the concentration of oxygen vacancies.
关键词： CuWO4,Mott-Hubbard model,Dielectric-dependent hybrid functionals,semiconducting oxide,oxygen vacancy,density functional theory (DFT)
更新于2025-09-19 17:15:36
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Evaluation of the relationship between the magnetism and the optical properties in SrTiO3-δ defective systems: Experimental and theoretical studies
摘要： To explore the relationship between optical properties, oxygen vacancies and magnetism in SrTiO3, we prepared a series of SrTiO3-δ (δ=0.00, 0.125 and 0.250) samples by solid state reaction method followed by the creation of oxygen vacancies-δ. Surface composition and chemical valence state in the synthesized compounds were examined by X-ray photoelectron spectroscopy (XPS). The Fourier Transform Infrared spectroscopy (FT-IR) spectra showed that the transmission properties change with oxygen vacancies introduction. Ultraviolet-visible absorption revealed that optical properties were highly dependent on oxygen vacancies concentrations. When the magnetic field was applied, magnetization showed weak-ferromagnetism at room temperature on SrTiO3-δ non-sto?chiometric systems. Yet, it was reversed showing diamagnetism on SrTiO3 perfect crystal. The large concentration of oxygen vacancies (δ=0.250) reduced ferromagnetism and optical absorption, implying the possible presence of a relationship between the magnetism and the optical properties. Theoretical results showed two types of electronic contributions to magnetism, one of which emanates from localized states below the conduction band minimum, and the other comes from itinerant electrons of Ti atoms lying further away from the oxygen-vacancy. The electronic structures and magnetic properties were calculated by Full-Potential Linear Augmented Plane Wave (FP-LAPW) method within the Generalized Gradient Approximation (GGA) and the atomic relaxations introduced by the oxygen vacancies host in a fully self-consistent way. The results shed some light on the promising magneto-optical properties of the SrTiO3-δ materials.
关键词： Density Functional Theory (DFT),Optical properties,Oxygen vacancy,SrTiO3,Magnetism
更新于2025-09-19 17:15:36
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[IEEE 2019 1st International Conference on Advances in Science, Engineering and Robotics Technology (ICASERT) - Dhaka, Bangladesh (2019.5.3-2019.5.5)] 2019 1st International Conference on Advances in Science, Engineering and Robotics Technology (ICASERT) - Effect of Solar Concentration on Performance of Perovskite Solar Cell: A detailed balance study
摘要： As a perovskite material, methylammonium lead iodide has become more popular for its flexibility, low-cost, lightweight, thin film and high power conversion capability in photovoltaic research community. In this work, we have explored the effect of solar concentration on PV performance for methylammonium lead iodide (CH3NH3PbI3) perovskite solar cell computationally. To calculate the band structure, bandgap and density of states (DOS) of CH3NH3PbI3, density functional theory (DFT) is used here. The detailed balance method is employed to figure out the effect of concentration on performance of perovskite solar cell. We have calculated performance parameters of CH3NH3PbI3 solar cell for two solar spectra AM 1.5 G and AM 1.5 D. All calculations have been performed at different solar concentrations ranging from no concentration to full concentration for both types solar spectra. It is found that the solar cell efficiency at 1.5 G spectrum is higher than 1.5 D solar spectrum at any solar concentration. These results may impact future research on perovskite solar cell.
关键词： Perovskite solar cell (PSC),solar concentration,PCE,density functional theory (DFT),detailed balance limit
更新于2025-09-16 10:30:52
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Enhanced Moisture Stability by Butyldimethylsulfonium Cation in Perovskite Solar Cells
摘要： Many organic cations in halide perovskites have been studied for their application in perovskite solar cells (PSCs). Most organic cations in PSCs are based on the protic nitrogen cores, which are susceptible to deprotonation. Here, a new candidate of fully alkylated sulfonium cation (butyldimethylsulfonium; BDMS) is designed and successfully assembled into PSCs with the aim of increasing humidity stability. The BDMS-based perovskites retain the structural and optical features of pristine perovskite, which results in the comparable photovoltaic performance. However, the fully alkylated aprotic nature of BDMS shows a much more pronounced effect on the increase in humidity stability, which emphasizes a generic electronic difference between protic ammonium and aprotic sulfonium cation. The current results would pave a new way to explore cations for the development of promising PSCs.
关键词： perovskites solar cells,humidity stability,density functional theory (DFT),butylammonium iodide,butyldimethylsulfonium iodide
更新于2025-09-12 10:27:22
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Photo-Switchable Boronic Acid Derived Salicylidenehydrazone Enabled by Photochromic Spirooxazine and Fulgide Moieties: Multiple Responses of Optical Absorption, Fluorescence Emission, and Quadratic Nonlinear Optics
摘要： A novel protocol of the boronic acid derived salicylidenehydrazone (BASHY) core being sandwiched by photochromic spirooxazine and fulgide moieties was proposed here to design multistate fluorescent photoswitches with variable nonlinear optical (NLO) responses. Systematic investigations on their optical absorption, fluorescence emission, and static first hyperpolarizabilities (β) were performed using density functional theory (DFT). It was found that the BASHY-based sandwiched series exhibited significant differences of absorption and emission properties between three photoisomers, which were essentially ascribed to the massive changes of corresponding electron transition characteristics quantified by hole–electron descriptors and visualized by electron density difference (EDD) plots. However, the isomerization of fulgide parts in the merocyanine (MC) form of spirooxazine failed to greatly shift maximum absorption/emission wavelengths, due to their high similarity of intrinsic transition features. Furthermore, large β contrasts between three photoisomers were observed, which resulted from significant variations of contributions of spirooxazine and/or fulgide moieties to the total β upon photoisomerization according to β densities. Although the fulgide moiety contributes negatively and positively to spirooxazine (SO) isomers when fulgide switches from close (C-) to open (E-) forms, respectively, their dominant βxxx values with opposite signs are still similar in magnitude, leading to quite close quadratic NLO responses. Therefore, the captivating ternary photoswitches with multiple responses of absorption, emission, and NLO were elaborately built in this context, promising to be applied as multifunctional optical materials in various scientific and technological fields.
关键词： photochromic spirooxazine,fulgide moieties,nonlinear optical (NLO) responses,density functional theory (DFT),boronic acid derived salicylidenehydrazone (BASHY)
更新于2025-09-12 10:27:22
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First-principle calculation of the electronic structures and optical properties of the metallic and nonmetallic elements-doped ZnO on the basis of photocatalysis
摘要： In the present paper, the electronic structure and the optical properties of metallic and nonmetallic elements-doped ZnO were investigated based on the principle of photocatalysis by first-principle density functional theory. Element doping shortens the band gap of ZnO. Due to the p-type characteristics, Fe, Cu, B and N doping brings impurity states over the Fermi level of ZnO, resulting in the shortening of the band gap, extending the absorption and utilization of solar light and thus enhancing the photocatalytic properties of ZnO. However, no impurity states appear in the band gap of Cd- and S-doped ZnO due to the intrinsic doping of Cd and S. Further investigations indicate that different doping atoms can indeed alter the near-Fermi level density of states (DOS) of ZnO and their electronic structures via substitution of zinc and oxygen atoms. In addition, the optical properties of ZnO are improved after doped with different atoms by comparing with those of pure ZnO. Due to the difference of their outer shell electrons of the doped atoms, the optical absorption properties of the investigated materials are followed as the following order: Fe-/B-doped ZnO>Cu-/N-doped ZnO>Cd-/S-doped ZnO>pure ZnO.
关键词： Doped ZnO,Density functional theory (DFT),Photocatalysis,First principle calculation
更新于2025-09-11 14:15:04
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Influence of Crystal Structure and 3d Impurities on the Electronic Structure of the Topological Material Cd3As2
摘要： This paper presents a theoretical study of the effects of crystal structure and Mn and Co substitutions for Cd on the electronic structure of the topological material Cd3As2. We have carried out density functional theory calculations of the band structure and density of states in tetragonal and cubic Cd3As2, as well as in Cd3 – xMnxAs2 and Cd3 – xCoxAs2 crystals. The results indicate that the band structure of the cubic Cd3As2 phase differs significantly from that of a Dirac semimetal, characteristic of the tetragonal phase. It has also been shown that, after Co substitution for 1/24 of the Cd atoms, the structure of the density of 3d electron states is similar to that of the density of states in the magnetic semiconductor Cd3 – xMnxAs2, with a characteristic minimum at the Fermi energy. At the same time, in the case of analogous Mn substitution for Cd, the density of d-electron states has no such minimum.
关键词： Mn,density functional theory (DFT) calculations,magnetic semiconductors,topological materials,Co,Cd3As2,Dirac semimetal,band structure,density of states (DOS)
更新于2025-09-10 09:29:36
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Half-Metallic Ferromagnetism Character in Cr-Doped CaS Diluted Magnetic Insulator and Semiconductor: an Ab Initio Study
摘要： The overall aim of this study is to investigate theoretically the structural, electronic, and magnetic properties of calcium sulfide (CaS) doped with chromium (Cr) impurity, in order to conduct a new search dilute magnetic semiconductors (DMS) suitable for different applications in electronics and spintronics. For measuring, the physical property of this compound is implemented using the first principles approach employed in WIEN2K code. The structural characteristics are optimized using the Generalized Gradient Approximation established by Perdew-Burk-Ernzerhof (PBE-GGA). We calculate and minimize the total energy of the three ternary compounds (Ca0.75Cr0.25S, Ca0.50Cr0.50S, and Ca0.25Cr0.75S) in the paramagnetic (PM), ferromagnetic (FM), and antiferromagnetic (AFM) phase. We find all compounds stable in (FM) structure, whereas the modified Becke and Johnson local density approximation (mBJ-LDA) functional has been employed to evaluate the electronic and magnetic properties. Based on our findings, indicate that this system revealed a half-metallic ferromagnetic behavior with half-metallic gap (HM) and 100% spin-polarized at the fermi level for all chromium (Cr) concentrations. This advantageous set of properties is due to the half-metallic behavior, where the majority spin and minority spin exhibit metallic and semiconducting behaviors respectively. The chromium atom is the most important source of the total magnetic moment in these compounds (4 μβ) by comparison with magnetic moments produced by Ca and S atoms, which have minor contribution. Finally, our prediction results require an experimental confirmation in the future.
关键词： Diluted magnetic insulators (DMI),Spintronics,CaS,HM ferromagnetism,Density functional theory (DFT)
更新于2025-09-10 09:29:36
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Theoretical study of charge-transport and optical properties of indeno[1,2- <i>b</i> ]fluorene-6,12-dione-based semiconducting materials
摘要： The conducting and optical properties of a series of indeno[1,2-b]fluorene-6,12-dione (IFD)-based molecules have been systematically studied and the influences of butyl, butylthio and dibutylamino substituents on the reorganization energies, intermolecular electronic couplings and charge-injection barriers of IFD have been discussed. The quantum-chemical calculations combined with electron-transfer theory reveal that the incorporation of sulfur-linked side chains decreases reorganization energy associated with hole transfer and optimizes intermolecular π–π stacking, which results in excellent ambipolar charge-transport properties (μh = 1.15 cm2 V?1 s?1 and μe = 0.08 cm2 V?1 s?1); in comparison, addition of dibutylamino side chains increases intermolecular steric interactions and hinders perfect intermolecular π–π stacking, which results in the weak electronic couplings and finally causes the low intrinsic hole mobility (μh = 0.01 cm2 V?1 s?1). Furthermore, electronic spectra of butyl-IFD, butylthio-IFD and dibutylamino-IFD were simulated and compared with the reported experimental data. Calculations demonstrate that IFD-based molecules possess potential for developing novel infrared and near-infrared probe materials via suitable chemical modifications.
关键词： intrinsic electron mobility,structure–function relationship,indeno[1,2-b]fluorene-6,12-dione-based molecules,density functional theory (DFT),intrinsic hole mobility,electronic spectra
更新于2025-09-09 09:28:46
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Energy Band Gap Modulation in Nd-doped BiFeO <sub/>3</sub> /SrRuO <sub/>3</sub> Heteroepitaxial for Visible Light Photoelectrochemical Activity
摘要： The ability of band offsets at multiferroic/metal and multiferroic/electrolyte interfaces in controlling charge transfer, and thus alters the photoactivity performance has sparked significant attention in solar energy conversion applications. Here, we demonstrate that the band offsets of the two interfaces play the key role in determining charge transport direction in a downward self-polarized BFO film. Electrons tend to move to BFO/electrolyte interface for water reduction. Our experimental and first-principles calculations reveal that the presence of neodymium (Nd) dopants in BFO enhances the photoelectrochemical performance by reduction of the local electron-hole pair recombination sites and modulation of the band gap to improve the visible light absorption. This opens a promising route to the heterostructure design by modulating the band gap to promote efficient charge transfer.
关键词： density functional theory (DFT),heterojunction band offsets,charge transfer,Nd-doped BiFeO3,photoelectrochemical (PEC)
更新于2025-09-04 15:30:14