Insights into structural,electronic, optical and thermoelectric properties of WB and WAlB: a first principle study

Detailed investigations on structural, electronic, optical and thermoelectric properties of WB and WAlB have been done by using a full-potential linearised augmented plane wave method. Different approximations have been used to treat the exchange–correlation potential. The PBEsol-GGA method is found to be the most suitable for WB and WAlB. The obtained values of the equilibrium structural parameters such as lattice constants, volume and bulk modulus are in good agreement with the available experimental and theoretical data. The results of electronic charge density plots show that WB has a strong covalent bond between B-B and an ionic bond between W-B. In case of WAlB, the distance between any two atoms is more than the corresponding interatomic distance in WB. The band structure and density of states around the fermi level suggest that WB has a metallic nature and WAlB has a semimetal-like character. The optical properties are determined and analysed in detail for the first time. The larger reflectivity in the low-energy region (infrared) indicates that these materials can be used as a coating material to remove solar heating. The effects of temperature on thermoelectric parameters are also studied for the first time. High value power factor and high thermal conductivity suggest that WB and WAlB are potential candidates for thermoelectric technological applications.     

First-principles study of structural,electronic and optical properties of ZnF_2

The structural, electronic, and optical properties of rutile-, CaC12-, and PdF2-ZnF2 are calculated by the plane-wave pseudopotential method within the density functional theory. The calculated equilibrium lattice constants are in reasonable agreement with the available experimental and other calculated results. The band structures show that the rutile-, CaCl2-, and PdF2-ZnF2 are all direct band insulator. The band gaps are 3.63, 3.62, and 3.36 eV, respectively. The contribution of the different bands was analyzed by the density of states. The Mulliken population analysis is performed. A mixture of covalent and weak ionic chemical bonding exists in ZnF2. Furthermore, in order to understand the optical properties of ZnF2, the dielectric function, absorption coefficient, refractive index, electronic energy loss spectroscopy, and optical reflectivity are also performed in the energy range from 0 to 30 eV. It is found that the main absorption parts locate in the UV region for ZnF2. This is the first quantitative theoretical prediction of the electronic and optical properties of ZnF2 compound, and it still awaits experimental confirmation.     

First principles study of electronic and optical properties of InAs

The electronic and optical properties of InAs in core-level spectra are calculated using the full-potential linearized augmented plane wave plus local orbitials (FP-LAPW +lo) method. The real and imaginary parts of the dielectric function ε(ω), the optical absorption coefficient I(ω), the reflectivity R(ω), the refractive index n(ω), and the extinction coefficient k(ω)are calculated. All these values are in good agreement with the experimental data. The effect of spin-orbit coupling on optical properties is also investigated and found to be quite small.      

Structural,elastic, electronic,optical and thermoelectric properties of the Zintl-phase Ae3AlAs3 (Ae = Sr,Ba)

First-principles calculations were performed to investigate the structural, elastic, electronic, optical and thermoelectric properties of the Zintl-phase Ae₃AlAs₃ (Ae = Sr, Ba) using two complementary approaches based on density functional theory. The pseudopotential plane-wave method was used to explore the structural and elastic properties whereas the full-potential linearised augmented plane wave approach was used to study the structural, electronic, optical and thermoelectric properties. The calculated structural parameters are in good consistency with the corresponding measured ones. The single-crystal and polycrystalline elastic constants and related properties were examined in details. The electronic properties, including energy band dispersions, density of states and charge-carrier effective masses, were computed using Tran-Blaha modified Becke-Johnson functional for the exchange-correlation potential. It is found that both studied compounds are direct band gap semiconductors. Frequency-dependence of the linear optical functions were predicted for a wide photon energy range up to 15 eV. Charge carrier concentration and temperature dependences of the basic parameters of the thermoelectric properties were explored using the semi-classical Boltzmann transport model. Our calculations unveil that the studied compounds are characterised by a high thermopower for both carriers, especially the p-type conduction is more favourable.     

Structural, electronic, and optical properties of ZnOl_xSex alloys using first-principles calculations

The structural, electronic, and optical properties of binary ZnO, ZnSe compounds, and their ternary ZnOl_xSex alloys are computed using the accurate full potential linearized augmented plane wave plus local orbital （FP-LAPW ＋ lo） method in the rocksalt （B 1） and zincblende （B3） crystallographic phases. The electronic band structures, fundamental energy band gaps, and densities of states for ZnO1_xSex are evaluated in the range 0 〈 x 〈 1 using Wu-Cohen （WC） generalized gradient approximation （GGA） for the exchange-correlation potential. Our calculated results of lattice parameters and bulk modulus reveal a nonlinear variation for pseudo-binary and their ternary alloys in both phases and show a considerable deviation from Vegard＇s law. It is observed that the predicted lattice parameter and bulk modulus are in good agreement with the available experimental and theoretical data. We establish that the composition dependence of band gap is semi-metallic in B1 phase, while a direct band gap is observed in B3 phase. The calculated density of states is described by taking into account the contribution of Zn 3d, O 2p, and Se 4s, and the optical properties are studied in terms of dielectric functions, refractive index, reflectivity, and energy loss function for the B3 phase and are compared with the available experimental data.     

First-principles study of structural,elastic, electronic and optical properties of RDX under pressure

ABSTRACT

The influences of pressure on structural, elastic, electronic and optical properties of α-RDX under pressure from 0 to 40?GPa have been investigated by performing first-principles calculations. The obtained structural parameters based on the GGA-PBE+G calculations are consistent with previous experimental values. The results of B/G, C₁₂-C₄₄ and Poisson's ratio show that α-RDX has changed to ductility under pressure between 0 and 5?GPa. The obvious rotation of NO₂ group in the equatorial position appears, especially in the range of pressure from 10 to 15?GPa, which influences the elastic and mechanical properties of α-RDX. Moreover, we find that the electrons of α-RDX become more active under higher pressure by comparing the curves of DOS under different pressure. Furthermore, the anisotropy of optical properties under different pressures has been shown.     

First-principles study of the electronic and optical properties of ZnO nanowires

The geometric, energetic, electronic structures and optical properties of ZnO nanowires (NWs) with hexagonal cross sections are investigated by using the first-principles calculation of plane wave ultra-soft pseudo-potential technology based on the density functional theory (DFT). The calculated results reveal that the initial Zn-O double layers merge into single layers after structural relaxations, the band gap and binding energies decrease with the increase of the ZnO nanowire size. Those properties show great dimension and size dependence. It is also found that the dielectric functions of ZnO NWs have different peaks with respect to light polarization, and the peaks of ZnO NWs exhibit a significant blueshift in comparison with those of bulk ZnO. Our results gives some reference to the thorough understanding of optical properties of ZnO, and also enables more precise monitoring and controlling during the growth of ZnO materials to be possible.     

First-principles study of the electronic structure and optical properties of cubic Perovskite NaMgF_3

The structural, electronic, and optical properties of cubic perovskite NaMgF3 are calculated by plane-wave pseudopo- tential density functional theory. The calculated lattice constant a0, bulk modulus B0, and the derivative of bulk modulus B~ are 3.872/~, 78.2 GPa, and 3.97, respectively. The results are in good agreement with the available experimental and theo- retical values. The electronic structure shows that cubic NaMgF3 is an indirect insulator with a wide forbidden band gap of Eg = 5.90 eV. The contribution of the different bands is analyzed by total and partial density of states curves. Population analysis of NaMgF3 indicates that there is strong ionic bonding in the MgF2 unit, and a mixture of ionic and weak covalent bonding in the NaF unit. Calculations of dielectric function, absorption coefficient, refractive index, electronic energy loss spectroscopy, optical reflectivity, and conductivity are also performed in the energy range 0 to 70 eV.     

First-principles studies of structural,mechanical, electronic,optical properties and pressure-induced phase transition of CuInO2 polymorph

Using the first-principles density-functional theory within the generalized gradient approximation (GGA), we have investigated the structural, elastic, mechanical, electronic, and optical properties and phase transition of CuInO₂. Structural parameters including lattice constants and internal parameter, pressure effects and phase transition pressure were calculated. We have obtained the elastic coefficients, bulk modulus, shear modulus, Young's modulus and Poisson's ratio. We find that two phases of CuInO₂ are indirect band gap semiconductors (F–Γ and H–Γ for 3R and 2H, respectively). Optical properties, including the dielectric function, refractive index, extinction coefficient, reflectivity, absorption coefficient, loss function and optical conductivity have been obtained for radiations of up to 30 eV.     

First-principles study of structural, mechanical, electronic and optical properties of 3R- and 2H-CuGaO2

We calculated the structural parameters, elastic, mechanical, electronic and optical properties of 3R- and 2H-CuGaO₂ using the first-principles density-functional theory. The results show that the structural parameters of two phases are in good agreement with previous theoretical and experimental data. Two phases are mechanically stable, behave in ductile manner and have indirect band gap. The analyses of electronic structures and charge densities of two phases show mainly covalent nature in Cu-O bonds and coexistence of both ionic and covalent nature in Ga-O bonds. The optical properties are obtained and discussed, including the complex dielectric function, refractive index, extinction coefficient, optical reflectivity, absorption coefficient, energy-loss spectrum and complex conductivity function, which provide useful information for the future applications of CuGaO₂.     

First-principles calculations for electronic, optical and thermodynamic properties of ZnS

The electronic, optical and thermodynamic properties of ZnS in the zinc-blende （ZB） and wurtzite （WZ） structures are investigated by using the plane-wave pseudopotential density functional theory （DFT）. The results obtained are consistent with other theoretical results and the available experimental data. When the pressures are above 20.5 and 27 GPa, the ZB-ZnS and the WZ-ZnS are converted into indirect gap semiconductors, respectively. The critical point structure of the frequency-dependent complex dielectric function is investigated and analysed to identify the optical transitions. Moreover, the values of heat capacity Cv and Debye temperature θ at different pressures and different temperatures are also obtained successfully.     

DFT study on electronic structures and optical absorption properties of C, S cation- doped SrTiO3

The effects of C cation and S cation doping on the electronic structures and optical properties of SrTiO₃ are investigated by density function theory (DFT) calculations. The calculated results reveal that the top of the valence band is predominately made up of the O 2p states for the pure SrTiO₃. When SrTiO₃ was doped with C cation and S cation, the top of the valence bands consists mainly of O 2p+C 2s hybrid orbitals and O 2p+S 3s hybrid orbitals, respectively. The band gap of SrTiO₃ is narrowed by the doping with C cation and S cation, especially for the C and S-codoped SrTiO₃. Moreover, the red shifts of the absorption edge are found by the calculated optical properties, which is consistent with reported experiment results. It is the explanation for their visible light respondency by the presence of C 2s and S 3s states on the upper edge of the valence band. All of these results can explain the good photocatalytic properties of C, S cation-codoped SrTiO₃ under visible light irradiation.      

反位缺陷对碳化硅纳米管电子结构和光学性质影响研究

采用基于密度泛函理论的第一性原理计算对含有反位缺陷（5,5）单壁碳化硅纳米管的电子结构和光学性质进行了研究.纳米管进行结构优化的结果显示,C_Si缺陷在纳米管表面形成了凹陷,Si_C缺陷形成了凸起;反位缺陷在纳米管的导带底附近形成了缺陷能级,使纳米管表现出n型导电的特点,由价带顶到缺陷能级的跃迁,在垂直和平行于纳米管管轴方向上形成了新的介电峰.     

An ab initio study of the structural,elastic, electronic and optical properties of the newly synthesized nitridoaluminate LiCaAlN2

The structural parameters, elastic constants, electronic structure and optical properties of the recently reported monoclinic quaternary nitridoaluminate LiCaAlN₂ are investigated in detail using the ab initio plane-wave pseudopotential method within the generalized gradient approximation. The calculated equilibrium structural parameters are in excellent agreement with the experimental data, which validate the reliability of the applied theoretical method. The chemical and structural stabilities of LiCaAlN₂ are confirmed by calculating the cohesion energy and enthalpy of formation. Chemical band stiffness is calculated to explain the pressure dependence of the lattice parameters. Through the band structure calculation, LiCaAlN₂ is predicted to be an indirect band gap of 2.725 eV. The charge-carrier effective masses are estimated from the band structure dispersions. The frequency-dependent dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity coefficient and electron energy loss function spectra are calculated for polarized incident light in a wide energy range. Optical spectra exhibit a noticeable anisotropy. Single-crystal and polycrystalline elastic constants and related properties, including isotropic sound velocities and Debye temperatures, are numerically estimated. The calculated elastic constants and elastic compliances are used to analyse and visualize the elastic anisotropy of LiCaAlN₂. The calculated elastic constants demonstrate the mechanical stability and brittle behaviour of the considered material.     

First-principles calculations for electronic and optical properties of the zinc-blende structured BeS compound under pressure

The electronic and the optical properties of the cubic zinc-blende (ZB) BeS under high pressure have been investigated by using \it ab initio plane-wave pseudopotential density functional theory method in the generalised gradient approximation (GGA) for exchange-correlation interaction. The electronic band structure and the pressure dependence of the total and partial densities of state under pressure are successfully described. Our calculations show that the ZB BeS has large and indirect band gaps associated with (Γ → X) transitions in ambient conditions. The results obtained are consistent with the experimental data available and other calculations. The optical properties, including dielectric function, energy-loss function, complex refractive index, reflection and absorption spectra, are investigated and analysed at different external pressures. The results suggest that the optical absorption appears mostly in the ultra-violet region and the curve of refractive index shift toward high energies (blue shift) with pressure increasing.     

Electronic structures and thermoelectric properties of solid solutions CuGa_(1-x) In_xTe_2 : A first-principles study

The electronic structures of solid solutions CuGal_xlnxTe2 are systematically investigated using the full-potential all-electron linearized augmented plane wave method. The calculated lattice parameters almost linearly increase with the increase of the In composition, which are in good agreement with the available experimental results. The calculated band structures with the modified Becke-Johnson potential show that all solid solutions are direct gap conductors. The band gap decreases linearly with In composition increasing. Based on the electronic structure calculated, we investigate the thermoelectric properties by the semi-classical Boltzmann transport theory. The results suggest that when Ga is replaced by In, the bipolar effect of Seebeck coefficient S becomes very obvious. The Seebeck coefficient even changes its sign from positive to negative for p-type doping at low carrier concentrations. The optimal p-type doping concentrations have been estimated based on the predicted maximum values of the power factor divided by the scattering time.     

Phase transition,electronic and optical properties of III-Sb compounds under pressure

III-V semiconductors are the backbone of optoelectronic industry. Here, we have performed first principle calculations to investigate the structural, electronic and optical properties of III-Sb (III = B, Al, Ga, Sb) compounds under the effect of pressure. The structural phase transition from zincblende to rocksalt phases is determined by the common tangent of the two E–V curves. The obtained results are in good agreement with the available literature. Compounds make electronic transition from semiconductors to metals under pressure. The calculated band structure in zincblende structure was compared with experimental and theoretical findings. Optical properties including real and imaginary parts of the complex dielectric function, frequency-dependent reflectivity and optical conductivity are explained to characterize the optical nature of these compounds in both phases.