First principles calculations of the structural,electronic and optical properties of the mixed fluorides SrxCd1−xF2

In the present work, we have investigated the structural, electronic and optical properties of SrF₂ and CdF₂ and their ternary mixed Sr_xCd_1?xF₂ alloys at some selected concentrations x (x?=?0.25, 0.50, 0.75 and 1). The parent compounds SrF₂ and CdF₂ crystallize in Fm-3?m space group, whereas the alloys adopt the cubic structure with Pm-3?m space group for the composition x?=?0.25 and 0.75 and the tetragonal structure with space group P4/mmm for x?=?0.50. The calculations were performed using the full-potential linearized augmented plane wave (FP-LAPW) method. The exchange-correlation potential was handled with Wu and Cohen GGA approximation (WC-GGA). Moreover, the Engel–Vosko's (EV-GGA) formalism and the modified Becke Johnson (mBJ) approximation were also applied to improve the electronic band structure calculations. The computed structural parameters for SrF₂ and CdF₂ such as the equilibrium lattice constants and the bulk moduli are in good agreement with the available experimental and theoretical data. It is found that the lattice parameters increase with increasing composition (x) while the bulk modulus decreases for Sr_xCd_1?xF₂ alloys. The calculated band structures reveal an indirect band gap (W-Γ), (X-Γ) and (M-Γ) for CdF₂, SrF_{2 and} Sr_xCd_1?xF₂ for x?=?0.25, 0.75 and x?=?0.5, respectively. The optical constants, including the dielectric function, refractive index, reflectivity, absorption, extinction coefficient and the energy loss function were calculated using both WC-GGA and mBJ schemes for a radiation up to 40?eV. This is the first quantitative theoretical prediction of the optical properties for these alloys that requires experimental confirmation.     

TB-mBJ calculation of structural,electronic and optical properties of two monovalent iodates AIO3 (A=Tl, α-Rb)

The Tran and Blaha modified Becke-Johnson potential TB-mBJ embedded in the WIEN2K code are used to calculate structural, electronic and linear optical properties of two isostructural iodates: TlIO₃ and α-RbIO₃. We have found that the computed structural properties are in good agreement with the experimental ones within a range error of [1.26–3.36%]. The investigated systems have indirect band gap of 3.32 eV and direct band gap of 3.82 eV respectively showing up their transparency within a considerable range of light. We also pointed out the ionic-covalent double character of Tl–O and Rb–O bonds. From linear optical considerations, we found that α-RbIO₃ is a better functional material than TlIO₃.     

Optical properties and electronic structure of fluorite and corundum

The complete sets of 12 fundamental optical functions for fluorite crystals in the range 5–39 eV and corundum crystals in the range 2–30 eV are determined from the experimental and theoretical spectra known for certain of these functions. The main features and generalities of these functions are revealed. A theoretical analysis of the optical spectra obtained is performed using the known theoretical band diagrams and the spectra of ?₂.     

Optical properties of Tl2In2Se3S layered single crystals

The optical properties of Tl₂In₂Se₃S layered single crystals have been analyzed using transmission and reflection measurements in the wavelength region between 500 and 1100 nm. The optical indirect transitions with a band gap energy of 1.96 eV and direct transitions with a band gap energy of 2.16 eV were determined from analysis of absorption data at room temperature. Dispersion of the refractive index is discussed in terms of the Wemple–DiDomenico single-effective-oscillator model. The refractive index dispersion parameters – oscillator energy, dispersion energy, oscillator strength and zero-frequency refractive index – were found to be 4.67 eV, 45.35 eV, 1.38 × 10¹⁴ m ^{? 2} and 3.27, respectively. Transmission measurements were also performed in the temperature range 10–300 K. As a result of temperature-dependent transmission measurements, the rate of change in the indirect band gap with temperature, i.e. γ = ?5.6 × 10^?4 eV/K, and the absolute zero value of the band gap energy, E _gi(0) = 2.09 eV, were obtained.     

Structural,electronic and optical properties of Ca3Bi2: First-principles investigation

In this work by applying first principles calculations structural, electronic and optical properties of Ca₃Bi₂ compound in hexagonal and cubic phases are studied within the framework of the density functional theory using the full potential linearized augmented plane wave (FP-LAPW) approach. According to our study band gap for Ca₃Bi₂ in hexagonal phase are 0.47, 0.96 and 1?eV within the PBE-GGA, EV-GGA and mBJ-GGA, respectively. The corresponding values for cubic phase are 1.24, 2.08 and 2.14?eV, respectively. The effects of hydrostatic pressure on the behavior of the electronic properties such as band gap, valence bandwidths and anti-symmetry gap are investigated. It is found that the hydrostatic pressure increases the band widths of all bands below the Fermi energy while it decreases the band gap and the anti-symmetry gap. In our calculations, the dielectric tensor is derived within the random phase approximation (RPA). The first absorption peak in imaginary part of dielectric function for both phases is located in the energy range 2.0–2.5?eV which are beneficial to practical applications in optoelectronic devices in the visible spectral range. For instance, hexagonal phase of Ca₃Bi₂ with a band gap around 1?eV can be applied for photovoltaic application and cubic phase with a band gap of 2?eV can be used for water splitting application. Moreover, we found the optical spectra of hexagonal phase are anisotropic along E||x and E||z.     

Electrical and material properties of hydrothermally grown single crystal (111) UO<Subscript>2</Subscript>

The semiconductor and optical properties of UO₂ are investigated. The very long drift carrier lifetimes, obtained from current–voltage I(V) and capacitance–voltage C(V) measurements, along with the well-defined optical properties provide little evidence of an abundance of material defects away from the surface region. Schottky barrier formation may be possible, but very much dependent on the choice of contact and surface stoichiometry and we find that Ohmic contacts are in fact favored. Depth resolved photoemission provided evidence of a chemical shift at the surface. Density functional theory, with the Heyd-Scuseria-Ernzerhof (HSE) functional, indicates a band gap of a 2.19 eV and an anti-ferromagnetic ground state. Ellipsometry measurements indicates at UO₂ is relatively isotropic with a band gap of approximately 2.0 eV band gap, consistent with theoretical expectations.     

Electronic and optical properties of defect chalcopyrite HgAl2Se4

The structural, electronic and optical properties of HgAl₂Se₄ are investigated using the full potential linear augmented plane wave method based on density functional theory. The calculated structural parameters using LDA are in excellent agreement with the available experimental result. The obtained energy band gap (2.24 eV) using EV-GGA approximation is in excellent agreement with experimental data (2.20 eV). Variation in the energy band gap as a function of the unit cell lattice parameter has been studied. The optical properties show a considerable anisotropy, which makes this compound very useful for various linear–nonlinear optical devices.     

The electronic structure and optical and magnetooptical properties of the CaCo<Subscript>2</Subscript> compound synthesized at a high pressure: Experiment and theory

The optical properties (the real ε₁ and imaginary ε₂ permittivity parts, optical conductivity σ, and reflectivity R) of the new ferromagnetic compound CaCo₂ in the Laves cubic phase (C15) synthesized at a pressure of 8.0 GPa were studied over the spectral range ?ω = 0.2–9 eV. The field and spectral (?ω = 0.5–4.2 eV) dependences of the equatorial Kerr effect were determined. The electronic structure and optical characteristics of CaCo₂ were calculated using the electron density functional theory by the linearized augmented-plane-wave method. The main band structure parameters of the compound were determined. The experimental and theoretical σ(ω) and R(ω) dependences were in satisfactory agreement with each other. The formation of the main absorption bands was found to be caused by the (p,d → d,p)-type electronic transitions related to the cobalt and calcium atoms. The exchange splitting of the 3d band of CaCo₂ was estimated, 2Δ_exc ～ (1–1.3) eV.     

Investigation of excitonic states effects on optoelectronic properties of Sb2Se3 crystal for broadband photo-detector by highly accurate first-principles approach

The rapid demand of photodetector is increasing day by day due to its versatility of applications that affect our lives. However, it is still very challenging to produce low-cost high-performance broadband photo-detector that can detect light from near infrared to the ultraviolet frequency range for medical diagnosis and visible light communication applications. Regarding this, low-cost antimony selenide (Sb₂Se₃), with direct energy gap and strong light absorption over a wider range from near infrared to ultraviolet frequency, is considered a promising candidate material for such kind of applications. Therefore, to expose its hidden potential, detailed analysis of its structural, electronic and optical properties is very essential. To accomplish this purpose, different schemes of the first-principles calculations are used in this study. Structural properties of Sb₂Se₃ are calculated by first-principles methods realized within density functional theory (DFT) framework. Whereas, to compute the quasiparticle (QP) band structure, excitonic and optical properties, many-body perturbation theory (MBPT) based on one-shot GW (G₀W₀) and Bethe-Salpeter equation (G₀W₀-BSE) approaches are used. Our DFT calculations show that Wu-Cohen GGA (WC-GGA) reproduces lattice parameters of Sb₂Se₃ material consistent with the experimental measurements. Similarly, G₀W₀ calculations confirm the Sb₂Se₃ a direct bandgap energy material of 1.32 eV and show good agreement with the experimental results. Similarly, the results on the optical properties of Sb₂Se₃ with the inclusion of electron-hole interaction show that the exciton energy of the material is 1.28eV while its corresponding plasma energy is 10.86 eV. These values show that the investigated material can absorb photons from near infrared to ultraviolet wavelengths. It is, therefore, anticipated that this material will be useful for new-generation optoelectronic applications from near infrared to ultraviolet wavelengths.     

Structural, electronic and optical properties of orthorhombic distorted perovskite TbMnO3

This paper calculates the structural parameters, electronic and optical properties of orthorhombic distorted perovskite-type TbMnO3 by first principles using density functional theory within the generalised gradient approximation. The calculated equilibrium lattice constants are in a reasonable agreement with theoretical and experimental data. The energy band structure, density of states and partial density of states of elements are obtained. Band structures show that TbMnO3 is an indirect band gap between the O 2p states and Mn 3d states, and the band gap is of 0.48 eV agreeing with experimental result. Furthermore, the optical properties, including the dielectric function, absorption coefficient, optical reflectivity, refractive index and energy loss spectrum are calculated and analysed, showing that the TbMnO3 is a promising dielectric material.     

Effect of cycle numbers on the structural,linear and nonlinear optical properties in Fe2O3 thin films deposited by SILAR method

Fe₂O₃ thin films were deposited by Successive Ionic Layer Adsorption and Reaction (SILAR) method onto glass substrates at different cycle numbers to investigate structural, linear and nonlinear optical properties. X-Ray Diffraction (XRD) analysis revealed that the Fe₂O₃ thin films have a non-crystalline nature. The morphological properties of the films were investigated by Field Emission-Scanning Electron Microscopy (FE-SEM) and the results show that the films’ surfaces are porous. The linear and nonlinear optical parameters were evaluated and analyzed by using transmittance and absorbance measurements. For these measurements, UV–Vis spectroscopy at room temperature was used. The refractive index values were calculated in the range of 1.45–3.23 for visible region (400–700 nm). Obtained results reveal that direct optical band gap changed between 2.62 and 2.68 eV and indirect optical band gap changed between 1.67 and 1.77 eV. Additionally, optical electronegativity, optical dielectric constants, surface and volume energy loss functions, nonlinear refractive index, linear optical susceptibility, third-order nonlinear optical susceptibility, optical and electrical conductivity, and loss tangent values were calculated and discussed in detail. It was found that each parameter studied is dependent on the cycle numbers. Also, it can be stated that Fe₂O₃ thin films are promising candidate for solar cells and optoelectronic device technology.     

First-principles study of structural, elastic, electronic, and optical properties of hexagonal BiAlO3

The structural parameters, elastic, electronic, and optical properties of hexagonal BiAlO₃ were investigated by the density functional theory. The calculated structural parameters are in good agreement with previous calculation and experimental data. The structural stability of BiAlO₃ has been confirmed by calculation of the elastic constants. The energy band structure, density of states, and Mulliken charge populations were obtained. BiAlO₃ presents an indirect band gap of 3.28 eV. Furthermore, the optical properties were calculated and analyzed. It is shown that BiAlO₃ is a promising dielectric material.     

Isotopic effects of the N(2D) + H2 → NH + H reaction: a quantum time-dependent wave packet investigation

Based on the potential energy surface reported by Li and co-workers (J. Comput. Chem. 34 1686–1696 (2013)), the dynamics calculations of N(²D)?+?H₂(v ₀?=?0, j ₀?=?0) reaction and its isotopic variants HD and D₂ are studied using time-dependent wave packet method in the collision energy range of 0.01–1.0?eV. Dynamics properties such as reaction probability, differential cross section, and integral cross section are studied at state-to-state level of theory. Present values are compared with available theoretical and experimental results. The results indicate that the integral cross sections of N(²D)?+?D₂ reaction are in general good agreement with the experimental data at collision energy below 0.15?eV. The rotational state-resolved integral cross sections of N(²D)?+?H₂/HD/D₂ reactions are compared with experimental values for the first time, with the obtained values being in good agreement with the experimental data.     

Impact of iron composition on the calculated electronic and magnetic properties of Fe3−xNixSi

ABSTRACT

The structural, electronic and magnetic properties of Fe_3?xNi_xSi alloys with variable iron composition (0?≤?x?≤?1) have been investigated within by using Projector augmented wave (PAW) method. The exchange–correlation potential was treated with the generalised gradient approximation (GGA) for the calculation of the structural properties and for the computation of the electronic and magnetic properties in order to treat the d states. These alloys crystallize in cubic Heusler structures; The Fe₃Si and Fe₂NiSi have a regular structure DO₃ and L2₁ respectively. To describe the experimental proprieties we use the on-site Coulomb interactions of U_eff(Ni)?=?3.1?eV and U_eff(Fe)?=?3.4?eV. A good agreement between calculated and experimental magnetic moments is found for the cubic Heusler phases without the addition of Hubbard-model. The obtained results of the density of states and the spin-polarized band structure show that the Fe₂NiSi alloy has half-metallic property. Through the obtained values of the total spin magnetic moment, we conclude that in general, the Fe₂NiSi alloy is half-metallic ferromagnet material whereas the Fe₃Si alloy has a metallic nature.     

Composition dependence of the optical properties and band structure of the zinc-blende ZnS1-xOx: a first principles study

We present first principles calculations of structural, electronic and optical properties of ZnS_1?xO_x in the zinc-blende phase. We employ the full potential linearized augmented plane wave method within the density functional theory in the generalized gradient approximation and Engel–Vosko generalized gradient approximation. Features such as the lattice constant, the bulk modulus and its pressure derivative are reported. The agreement between our calculated results and available experimental and theoretical data is generally good. Direct and indirect energy band gaps as a function of the oxygen composition in the material of interest are presented and discussed. The material under investigation is found to remain a direct band gap semiconductor over all the alloy composition range (0–1). Furthermore, the optical properties such as the dielectric function, the refractive index, the reflectivity and the electron loss energy have also been reported and analysed.     

Theoretical investigations of the structural,electronic and optical properties of Hg1−xCdxTe alloys

The structural, electronic and optical properties of mercury cadmium telluride (Hg_1?xCd_xTe; x = 0.0, 0.25, 0.5, 0.75) alloys are studied using density functional theory within full-potential linearized augmented plane wave method. We used the local density approximation (LDA), generalized gradient approximation (GGA), hybrid potentials, the modified Becke–Johnson (LDA/GGA)-mjb and Hubbard-corrected functionals (GGA/LDA + U), for the exchange-correlation potential (E_ex). We found that LDA functional predicts better lattice constants than GGA functional, whereas, both functionals fail to predict the correct electronic structure. However, the hybrid functionals were more successful. For the case of HgTe binary alloy, the GGA + U functional predicted a semi-metallic behaviour with an inverted band gap of ?0.539 eV, which is closest to the experimental value (?0.30 eV). Ternary alloys, however, are found to be semiconductors with direct band gaps. For the x = 0.25 and 0.50, the best band gaps are found to be 0.39 and 0.81 eV using LDA-mbj functional, whereas, the GGA-mbj functional predicted the best band gap of 1.09 eV for Hg_0.25Cd_0.75Te alloy, which is in a very good agreement with the experimental value (1.061 eV). The optical properties of the alloys are obtained by calculating the dielectric function ?(ω). The peaks of the optical dielectric functions are consistent with the electronic gap energies of the alloys.     

Mechanical,electronic and optical properties of SeZnO3: a GGA+U study

ABSTRACT

Based on first principles computations, the structural, mechanical, electronic band structure, and optical properties of SeZnO₃ compound have been predicted. The dependence of selected observables of SeZnO₃ compound on the effective U (the Hubbard on-site Coulomb repulsion) parameter has been investigated in detail. The elastic constant, Young’s modulus, bulk modulus, shear modulus, Poisson ratio, anisotropic factor, acoustic velocity, and Debye temperature have been computed. The calculated electronic band structure and density of states indicate that SeZnO₃ is a semiconductor material and has indirect band gap. The computations of the optical spectra, as a function of the incident photon radiation in 0–35?eV energy range has also been performed and the interband transitions are examined. The results indicate that Hubbard parameter plays a crucial role in explaining mechanical, electronic, and optical properties of SeZnO₃.     

Ellipsometric characterization of PbI2 thin film on glass

The optical properties of polycrystalline lead iodide thin film grown on Corning glass substrate have been investigated by spectroscopic ellipsometry. A structural model is proposed to account for the optical constants of the film and its thickness. The optical properties of the PbI₂ layer were modeled using a modified Cauchy dispersion formula. The optical band gap E_g has been calculated based on the absorption coefficient (α) data above the band edge and from the incident photon energy at the maximum index of refraction. The band gap was also measured directly from the plot of the first derivative of the experimental transmission data with respect to the light wavelength around the transition band edge. The band gap was found to be in the range of 2.385±0.010 eV which agrees with the reported experimental values. Urbach's energy tail was observed in the absorption trend below the band edge and was found to be related to Urbach's energy of 0.08 eV.     

Theoretical Study of the Structural,Electronic, Chemical Bonding and Optical Properties of the A2<Subscript>1</Subscript><Emphasis Type="Italic">am</Emphasis> Orthorhombic SrBi<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>9</Subscript>

The structural parameters, density of states, electronic band structure, charge density, and optical properties of orthorhombic SrBi₂Ta₂O₉ have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principle density functional theory (DFT). The calculated structural parameters were in agreement with the previous theoretical and experimental data. The band structure showed an indirect (S to Γ) band gap with 2.071 eV. The chemical bonding along with population analysis has been studied. The complex dielectric function, refractive index, and extinction coefficient were calculated to understand the optical properties of this compound, which showed an optical anisotropy in the components of polarization directions (100), (010), and (001).     

Controlling the stability and the electronic structure of transition metal dichalcogenide single layer under chemical doping

By means of ab initio calculation based on density-functional theory (DFT), we have investigated the electronic and optical properties of single layer MoSe₂ under chemical doping by various groups, such as ?H, ?OH, ?NH₂ and ?CH₃. This work is generalized for all polymorph 1H, 1T, 1T′ and the new investigated phase 1T″. We found that all those functional groups (FG) bonded covalently to the chalcogen atom (Se). The evaluation of adsorption energy shows that the hydrogen atom binds more strongly than other functional groups in particular with the T phase. Furthermore, the attachment of functional groups to T-MoSe₂ leads to dramatic changes to the structure stability and the optoelectronic properties of the material by tuning its band gap from metallic to a semiconductor. Also, we found that the band gap is strongly depending on the type and the densities of dopants.