Electronic structure, charge density, and chemical bonding properties of C11H8N2O o-methoxydicyanovinylbenzene (DIVA) single crystal

A comprehensive theoretical density functional theory (DFT) study of the electronic crystal structure, bonding properties, electron charge density of C₁₁H₈N₂O o-methoxydicyanovinylbenzene (DIVA) single crystals were performed. The exchange and correlation potential was described within a framework of the local density approximation (LDA) by Ceperley-Alder and gradient approximation (GGA) based on exchange–correlation energy optimization to calculate the total energy. In addition, we have used Engel–Vosko generalized gradient approximation (EV-GGA) and the modified Becke–Johnson potential (mBJ) for the electronic crystal structure, bonding properties, electron charge density calculations. There is systematically increasing in the energy gap from 2.25 eV (LDA), 2.34 eV (GGA), 2.50 eV (EV-GGA), 2.96 eV (mBJ). Our calculations show that this crystal possess direct energy gap. Furthermore, the electronic charge density space distribution contours in the (1 1 0) crystallographic plane clarifies the nature of chemical bonding.     

Dispersion of the linear and nonlinear optical susceptibilities of disilver germanium sulfide from DFT calculations

The dispersion of the linear and nonlinear optical susceptibilities is calculated for disilver germanium sulfide (Ag₂GeS₃) using the all-electron full potential linearized augmented plane wave (FP-LAPW) method. Calculations are performed with four exchange correlations namely local density approximation (LDA), general gradient approximation (GGA), Engel–Vosko generalized gradient approximation (EVGGA), and modified Becke–Johnson potential (mBJ). Our calculations give a band gap of 0.40 eV (LDA), 0.42 eV (GGA), 1.03 eV (EVGGA), and 1.30 eV (mBJ) in comparison with our measured gap (1.98 eV). The mBJ exchange correlation gives the best agreement with experiment. We find that the calculated linear optical susceptibilities of Ag₂GeS₃ show considerable anisotropy which is useful for second harmonic generation and optical parametric oscillation. To analyze the spectra of the calculated χ ₁₁₃ ⁽²⁾ (ω), χ ₂₃₂ ⁽²⁾ (ω), χ ₃₁₁ ⁽²⁾ (ω), χ ₃₂₂ ⁽²⁾ (ω), and χ ₃₃₃ ⁽²⁾ (ω), we have correlated the features of these spectra with the features of ?₂(ω) spectra as a function of ω/2 and ω. From the calculated dominant component |χ ₃₃₃ ⁽²⁾ (ω)|, we find that the microscopic second-order hyperpolarizability, β₃₃₃, the vector components along the dipole moment direction is 41.2 × 10^?30 esu at static limit and 222.9 × 10^?30 esu at λ = 1064 nm.     

Electronic and optical properties of the orthorhombic compounds FeX2 (X = P,As and Sb)

First principles calculations, by means of the full-potential linearized augmented plane wave (FP-LAPW) method within the local density approximation (LDA), were carried out for the structural, electronic and optical properties of the orthorhombic compounds FeP₂, FeAs₂ and FeSb₂. The structural properties are determined through the total energy minimization and the relaxation of the internal parameters. The modified Becke–Johnson (mBJ) method is applied for the electronic structure of FeSb₂. Our LDA-calculation shows that the first two compounds are indirect-gap semiconductors, while for the third one it predicts a small hole-pocket at the R point. The mBJ gives a semiconducting state with an indirect energy gap of 0.248 eV for FeSb₂. The overall shape of the calculated imaginary parts of the dielectric tensor is similar for the three compounds. The assignment of the structures in the optical spectra and band structure transitions are investigated. The electronic dielectric constant along (0 1 0) direction is the largest for the three compounds. For FeAs₂, the calculated components of reflectivity have the same trend of variation as the measured ones in the energy range 1.54–3.1 eV.     

Optoelectronic and thermoelectric properties of KAuX5 (X = S, Se): a first principles study

The electronic structure as well as optical and thermoelectric properties of the orthorhombic polychalcogenides of gold KAuX₅ (X = S, Se) compounds have been investigated using full-potential linearized augmented plane wave within the framework of the density functional theory (DFT). The local density approximation (LDA), generalized gradient approximation (GGA) by Perdew, Burke and Ernzerhof (PBE), Engel–Vosko generalized gradient approximation (EV-GGA), and the recently modified Becke–Johnson approximation (mBJ) formalism are used for the exchange correlation energy to calculate the total energy. The results show that KAuX₅ (X = S, Se) is a direct band gap semiconductor at Γ–Γ point. The total and partial density of states indicate that the states Au-d, S-p, and Se-p of both compounds have strong contributions to valence band in the energy range from ?10 up to 0.0 eV. One can notice from electronic charge density that both compounds show greater iconicity and smaller covalency. Optical properties with photon incident energy up to 14.0 eV have been calculated and analyzed. Important transport properties such as Seebeck coefficients as well as thermal and electrical conductivities and effective mass are obtained and discussed in details.     

Electronic structure of alkali-metal/alkaline-earth-metal fluorine beryllium borate NaSr3Be3B3O9F4 single crystal: DFT approach

The electronic band structure, total and angular momentum resolved projected density of states for NaSr₃Be₃B₃O₉F₄ are calculated using the all-electron full potential linearized augmented plane wave plus local orbitals (FP-LAPW + lo) method. The calculations are performed within four exchange correlations namely; local density approximation (LDA), general gradient approximation (PBE-GGA), Engel–Vosko generalized gradient approximation (EVGGA) and the recently modified Becke–Johnson potential (mBJ). Calculations suggest that NaSr₃Be₃B₃O₉F₄ is a direct wide band gap semiconductor. The exchange correlations potentials exhibit significant influence on the value of the energy gap being about 4.82 eV (LDA), 5.16 eV (GGA), 6.20 (EVGGA) and 7.20 eV (mBJ). The mBJ approach succeed by large amount in bringing the calculated energy gap closer to the experimental one (7.28 eV). The angular momentum resolved projected density of states shows the existence of a strong hybridization between the various orbitals. In additional we have calculated the electronic charge density distribution in two crystallographic planes namely (1 0 1) and (0 0 −1) to visualized the chemical bonding characters.     

First-principles study of the electronic,optical and bonding properties in dolomite

The structural, electronic, optical properties and chemical bonding of dolomite CaMg(CO₃)₂ (rhombohedral calcite-type structure) are investigated using plane wave pseudopotential density-functional theory (DFT) method taking the local density approximation (LDA) and the generalized gradient approximation (GGA) as the exchange–correlation energy functional. The structural properties are consistent with the early experimental and theoretical results. The indirect electronic band gap is estimated to be ～5.0 eV, which is less than the optical band gap measured from the fundamental absorption edge of ～6.0 eV. The optical band gap is also consistent with the experimental band gap of similar calcite-type structure. A noticeable difference for the LDA and GGA derived transition peaks and a significant optical anisotropy are observed in the optical spectra. The analysis of electronic density of states, Mulliken charge and bonding population shows the coexistence of covalent and ionic bonding in the dolomite structure and the results are consistent with previous theoretical calculations.     

First-principles study of electronic and optical properties of Pbnm orthorhombic SrHfO3

The first-principles calculations were carried out to investigate the electronic and optical properties of Pbnm orthorhombic SrHfO₃. The equilibrium lattice constants of Pbnm orthorhombic SrHfO₃ optimized by the localized density approximation (LDA) are in good agreement with experimental values. Electronic structures of Pbnm orthorhombic SrHfO₃ have been studied throughout the calculations of band structure, densities of states (DOS) and charge densities. The band structure shows that Pbnm orthorhombic SrHfO₃ has direct band gap. The DOS and charge densities of Pbnm orthorhombic SrHfO₃ indicate that bonding between Hf and O is mainly covalent whereas bonding between Sr and O is mainly ionic. The complex dielectric function, refractive index, absorption coefficient, energy-loss spectrum, complex conductivity function and reflectivity of Pbnm orthorhombic SrHfO₃ have been predicted. The imaginary and real parts of the calculated complex dielectric function are consistent with the experimental measurements for the amorphous SrHfO₃.     

Elastic, optoelectronic, and thermal properties of cubic CSi2N4: an ab initio study

The mechanical, optoelectronic, and thermodynamic properties of carbon silicon nitride spinel compound have been investigated using density functional theory. The exchange–correlation potential was treated with the local density approximation (LDA) and the generalized gradient approximation of Perdew–Burke and Ernzerhof (PBE-GGA). In addition, the Engel–Vosko generalized gradient approximation (EV-GGA) and the modified Becke–Johnson potential (TB-mBJ) were also applied to improve the electronic band structure calculations. The ground state properties, including lattice constants and bulk modulus, are in fairly good agreement with the available theoretical data. The elastic constants, Young’s modulus, shear modulus, and Poisson’s ratio have been determined by using the variation of the total energy with strain. From the elastic parameters, it is inferred that this compound is brittle in nature. The results of the electronic band structure show that CSi₂N₄ has a direct energy band gap (Γ–Γ). The TB-mBJ approximation yields larger fundamental band gaps compared to those of LDA, PBE-GGA, and EV-GGA. In addition, we have calculated the optical properties, namely, the real and the imaginary parts of the dielectric function, refractive index, extinction coefficient, reflectivity, and energy loss function for radiation up to 40.0 eV. Using the quasi-harmonic Debye model which considers the phononic effects, the effect of pressure P and temperature T on the lattice parameter, bulk modulus, thermal expansion coefficient, Debye temperature, and the heat capacity for this compound were investigated for the first time.     

Density of electronic states and dispersion of optical functions of defect chalcopyrite CdGa2X4 (X = S,Se): DFT study

A density functional theory (DFT) based on full potential linear augmented plane wave (FPLAPW) was used for calculating the electronic structure, charge density and optical properties of CdGa₂X₄ (X = S, Se) compounds. Local density approximation (LDA), generalized gradient approximation (GGA), Engle Vasko generalized gradient approximation (EVGGA) and recently modified Becke–Johnson (mBJ) were applied to calculate the band structure, total and partial density of states. The investigation of band structures and density of states of CdGa₂X₄ (X = S, Se) elucidate that mBJ potential show close agreement to the experimental results. The mBJ potential was selected for further explanation of optical properties of CdGa₂X₄ (X = S, Se). The study of electronic charge density contours shows that change in the bond lengths and bond nature affect the band gap of the compounds. The two non-zero dielectric tensor components and its derivatives show considerable anisotropy between the perpendicular and parallel components. The present work provide accurate information about the combination (hybridization) of orbital, formation of bands and dispersion of non-zero tensor components of CdGa₂X₄ (X = S, Se).     

Electronic and optical properties of orthorhombic LiInS2 and LiInSe2: A density functional theory investigation

The structural, electronic and optical properties of two orthorhombic crystals, LiInS₂ and LiInSe₂, were calculated using the density functional theory. The optimized unit cells are in good agreement with experimental data. It is shown that the two crystals belong to the semiconductors with a direct energy band gap of about 3.17 eV for LiInS₂ and 2.63 eV for LiInSe₂. The important structural character of the two compounds is that there is a strong hybridization between In-5s, 5p orbits and S-3p (Se-4p) orbits at upper valence bands. The fundamental understanding on how the different anion (Se and S) affects the electronic and optical properties of the two crystals was highlighted in our calculations. The optical properties include the dielectric spectra, absorption, reflectivity and energy-loss spectra, and the origin of spectral peaks were analyzed based on the electronic structures. The results indicate that the two compounds are promising IR crystal materials.     

Synthesis and characterization of low particle size nanocrystalline SnSe thin films

Tin selenide (SnSe) nanocrystalline thin films of different thickness from 15 to 70 nm were prepared by inert gas condensation technique. Argon gas flow and substrate temperature were kept constant during deposition process at 2 × 10^?3 Torr and 27 °C respectively. Polycrystalline orthorhombic phase structured was deduced for the prepared SnSe ingot powder by X-ray diffraction pattern. The grazing incident in-plane X-ray diffraction (GIIXD) pattern showed nanocrystalline orthorhombic structure for deposited SnSe thin film. The TEM micrographs showed that thin films were nanocrystalline with particle size in the range from 2 to 5.7 nm. The optical band gap E_g of the thin films due to direct allowed transition have values ranging from 2.5 to 2.13 eV as the particle size increases from 2 to 5.7 nm. The photoconductivity spectra of the nanostructured SnSe thin films of different particle size showed transitions at 2.45, 2.34 and 2.21 eV for films of different particle size.     

Effect of annealing temperature on optical and electrical properties of ZrO2–SnO2 nanocomposite thin films

ZrO₂–SnO₂ nanocomposite thin films were deposited onto quartz substrate by sol–gel dip-coating technique. Films were annealed at 500, 800 and 1,200 °C respectively. X-ray diffraction pattern showed a mixture of three phases: tetragonal ZrO₂ and SnO₂ and orthorhombic ZrSnO₄. ZrSnO₄ phase and grain size increased with annealing temperature. Fourier transform infra-red spectroscopy spectra indicated the reduction of –OH groups and increase in ZrO₂–SnO₂, by increasing the treatment temperature. Scanning electron microscopy observations showed nucleation and particle growth on the films. The electrical conductivity decreased with increase in annealing temperature. An average transmittance greater than 80 % (in UV–visible region) was observed for all the films. The optical constants of the films were calculated. A decrease in optical band gap from 4.79 to 4.59 eV was observed with increase in annealing temperature. Photoluminescence (PL) spectra revealed an emission peak at 424 nm which indicates the presence of oxygen vacancy in ZrSnO₄. PL spectra of the films exhibited an increase in the emission intensity with increase in temperature which substantiates enhancement of ZrSnO₄ phase and reduction in the non-radiative defects in the films. The nanocomposite modifies the structure of the individual metal oxides, accompanied by the crystallite size change and makes it ideal for gas sensor and optical applications.     

Rutile TiO<Subscript>2</Subscript> films as electron transport layer in inverted organic solar cell

Titanium dioxide (TiO₂) thin films were prepared by sol–gel spin coating method and deposited on ITO-coated glass substrates. The effects of different heat treatment annealing temperatures on the phase composition of TiO₂ films and its effect on the optical band gap, morphological, structural as well as using these layers in P3HT:PCBM-based organic solar cell were examined. The results show the presence of rutile phases in the TiO₂ films which were heat-treated for 2 h at different temperatures (200, 300, 400, 500 and 600 °C). The optical properties of the TiO₂ films have altered by temperature with a slight decrease in the transmittance intensity in the visible region with increasing the temperature. The optical band gap values were found to be in the range of 3.28–3.59 eV for the forbidden direct electronic transition and 3.40–3.79 eV for the allowed direct transition. TiO₂ layers were used as electron transport layer in inverted organic solar cells and resulted in a power conversion efficiency of 1.59% with short circuit current density of 6.64 mA cm^?2 for TiO₂ layer heat-treated at 600 °C.     

Structural, chemical, and optical properties of tin sulfide thin films as controlled by the growth temperature during co-evaporation and subsequent annealing

Tin sulfide thin films on soda-lime glass substrate were prepared by co-evaporation. This technique uses a vapor phase procedure involving chemical reactions between the precursor species evaporated simultaneously. The influence of the substrate temperature in the crystal structure and chemical composition were determined by X-ray diffraction and energy dispersive analysis of X-rays, showing that thin films crystallized in SnS, SnS₂, and Sn₂S₃ phases. Scanning electron microscope shows thin films with homogenous and uniform surface. Some of the samples were annealed to study the variation of structural, chemical, and optical properties. The variation of refractive index (n), extinction coefficient (k), and dielectric constant (ε) with wavelength and photon energy are reported. The energy band gap was calculated from optical transmittance and reflectance measurements in the range 300–1500 nm. The calculated energy band gap values were between 1.75 and 2.3 eV, depending on the phase in which crystallized the different thin films.     

First-Principles Prediction of Structural,Magnetic, Electronic,and Elastic Properties of Full-Heusler Compounds Co<Subscript>2</Subscript>YIn (Y = Ti,V)

Density functional theory based on the full-potential linearized augmented plane wave (FP-LAPW) method is used to investigate the structural, magnetic, electronic, and elastic properties of Heusler alloys Co₂YIn (Y = Ti, V). It is shown that the calculated spin magnetic moments using the local spin-density approximation (LSDA), generalized gradient approximation (GGA), LSDA + U, and Tran–Blaha (TB)-modified Becke–Johnson (mBJ)-local density approximations (LDA) are in good agreement with the Slater–Pauling rule. The obtained results with LSDA, GGA-PBE, and LSDA + U of the density of states illustrate that both compounds have a metal behavior; however, mBJ-LDA predicts Co₂VIn alloy to be a half metal. The band structure obtained with mBJ-LDA has an indirect band gap along the Γ–X symmetry with energy of 0.4 eV for Co₂VIn, and E _F lies in the middle of the gap; the electrons at the Fermi level are fully spin-polarized. The calculation of elastic properties indicates the stability of these compounds, and they have a ductile behavior. The 3D dependences of Young’s modulus exhibit a strong anisotropic character. The high values of the elastic constant C ₁₁ reflect the strength of the bonding Ti (V)–In.     

Structural, Optical and Magnetic Properties of Multiferroic GdMnO3 Nanoparticles

The structural, optical, and magnetic properties of multiferroic GdMnO₃ nanoparticles synthesized by the modified sol–gel route have been investigated. Raman spectroscopy and X-ray diffraction along with Rietveld refinement confirm the pure phase of the GdMnO₃ nanoparticles having an orthorhombic perovskite (space group: Pnma) type structure. The morphology was examined by scanning electron microscopy. Energy dispersive spectroscopy confirms the stoichiometry of the composition. The room temperature UV-visible absorption spectrum using Tauc’s relation gives an optical band gap of ～2.9 eV. A magnetization study of the GdMnO₃ nanoparticles was performed over a temperature range of 2–300 K at an applied field of 0.05 T by using a vibrating sample magnetometer. An effective magnetic moment (μ _eff) of ～9.2μ _B was obtained. The system is paramagnetic at room temperature and shows a ferromagnetic-like nature at 2 K as the applied magnetic field aligns the Gd moments and the contribution of the net moment of Gd spins is larger than that of the anti-ferromagnetically canted state of the Mn spins.     

Temperature-induced modification on the structural, optical and morphological properties of Zn0.96Cu0.04O nanoparticles

Zn_0.96Cu_0.04O nanoparticles synthesized by co-precipitation method were annealed at different temperatures, 400, 500, 600 and 700 °C for 2 h in air atmosphere. Crystalline phases and optical studies of the nanoparticles were studied by X-ray diffraction (XRD) and ultraviolet (UV)–visible photo-spectrometer. Elemental composition was studied by the energy dispersive X-ray (EDX) analysis and the microstructure was examined by scanning electron microscope. The XRD showed that the prepared nanoparticles had different microstructure without changing a hexagonal wurtzite structure. The average crystallite size increased from 28 to 60 nm when the annealing temperatures increased from 400 to 700 °C. The EDX analyses confirmed the presence of Cu in ZnO system and the weight percentage was nearly equal to their nominal stoichiometry within the experimental error. The optical band gap was varied between 3.75 and 3.86 eV and found maximum, 3.86 eV at 500 °C. Existence of functional groups and bonding were analyzed by fourier transform infrared spectra. The observed blue shift in UV emission from 400 to 500 °C in photoluminescence spectra was due to the intrinsic and extrinsic impurities whereas the red shift after 500 °C was due to the increase of crystalline size and relaxation of tensile strain. The reduction in intensity of green band emission with temperature was due to the reduction of intrinsic and extrinsic defects in Zn–O–Cu lattice.     

Structural,electronic properties and charge density distribution of the LiNaB4O7: Theory and experiment

The title compound was synthesized by employing high-temperature solution reaction methods at 840 °C. Single-crystal XRD analysis showed that it crystallizes in the orthorhombic noncentrosymmetric space group Fdd2, with unit cell parameters a = 13.326(3) Å, b = 14.072(3) Å, c = 10.238(2) Å, Z = 16, and V = 1919.9(7) Å³. It has two independent and interpenetrating 3D frameworks consisting of [B₄O₉]⁶⁻ groups bridged by O atoms, with intersecting channels occupied by Na⁺ and Li⁺ cations. The IR spectrum further confirmed the presence of both BO₃ and BO₄ groups. UV–vis diffuse reflectance spectrum showed a band gap of about 3.88 eV. Solid-state fluorescence spectrum exhibited the maximum emission peak at around 337.8 nm. Furthermore we have performed theoretical calculations by employing the state-of-the-art all-electron full potential linearized augmented plane wave (FP-LAPW) method to solve the Kohn Sham equations. We have optimized the atomic positions taken from our XRD data by minimizing the forces. The optimized atomic positions are used to calculate the electronic band structure, the atomic site-decomposed density of states, electron charge density and the chemical bonding features. The calculated electronic band structure and densities of states suggested that this single crystal possesses a wide energy band gap of about 2.80 eV using the local density approximation, 2.91 eV by generalized gradient approximation, 3.21 eV for the Engel–Vosko generalized gradient approximation and 3.81 eV using modified Becke–Johnson potential (mBJ). This compares well with our experimentally measured energy band gap of 3.88 eV. From our calculated electron charge density distribution, we obtain an image of the electron clouds that surround the molecules in the average unit cell of the crystal. The chemical bonding features were analyzed and the substantial covalent interactions were observed between O and O, B and O, Li and O as well as Na and O atoms.     

Crystal structure,optical behavior and electrical conduction of the new organic–inorganic compound CH<Subscript>3</Subscript>NH<Subscript>3</Subscript>CdI<Subscript>3</Subscript>

A new organic–inorganic compound CH₃NH₃CdI₃ (MACdI₃) was prepared by solvent diffusion method. Single crystal diffraction results showed that MACdI₃ had a monoclinic system with P2₁/c space group at room temperature. UV–Visible absorption spectra revealed that the optical band gap (\({E_g}\)) of 3.45 eV is in agreement with the theoretical value. Band structure and density of states calculations indicated that the valence band is mainly iodine 5p in character and the conduction band is the interaction between Cd 4d in character and iodine 5p states. The temperature dependent dielectric constant and alternating current (AC) conduction analysis displayed a phase transition at about 348 K, which could be confirmed by temperature dependent Raman spectra. AC conduction results demonstrated that the conduction in MACdI₃ was attributed to correlated barrier hopping at 308–348 K and non-overlapping small polaron tunneling at 348–398 K.     

Structural, optical and electrical characterization of selenium sulphide nanostructured thin film

Thin film of selenium sulphide (Se₇₅S₂₅) has been prepared using inert-gas consolidation (IGC) method and micro-structural, optical and electrical measurements were carried out on the film. Scanning electron microscopy (SEM) studies show that the deposited film is well adherent and grains are uniformly distributed over the surface of the substrate. X-ray diffraction (XRD) analysis shows that the film is polycrystalline nature with single phase and crystallizes in the orthorhombic structure. The field emission transmission electron microscope (FETEM) revealed the uniform dispersion and an average particle size of 20 nm. Analysis of the optical absorption data indicates that the optical band gap E_opt of this film obeys Tauc's relation for the allowed non-direct transition with energy gap is 2.48 eV. Electrical conduction measurements also show the presence of two distinct phases of the materials and characteristic changes in transport properties due to the nanosize of the materials.