First principles study of structural,electronic and optical properties of AgSbS2

In this work, we study the structural, electronic and optical properties of AgSbS₂, using full-potential linearized augmented plane wave and the pseudopotential plane wave scheme in the frame of generalized gradient approximation. Features such as the lattice constant, bulk modulus and its pressure derivative are reported. Our results suggest a phase transition from AF-IIb phase to rocksalt (B1) phase under high pressure. The calculated band structure and density of states show that the material under load has an indirect energy band gap X→(LГ) for AF-IIb phase (semiconductor) and a negative band gap W→(ГX) for B1 phase (semimetal). The optical properties are analyzed and the origin of some peaks in the spectra is discussed. Besides, the dielectric function, refractive index and extinction coefficient for radiation up to 14 eV have also been reported and discussed.     

Ab initio prediction of structural,electronic, magnetic and optical properties of Ba2GdSbO6

A first-principles approach is used to study the structural, electronic, optic and magnetic properties of Ba₂GdSbO₆, using full-potential linearized augmented plane wave (FP-LAPW) scheme within GGA+U approach. Features such as the lattice constant, bulk modulus and its pressure derivative are reported. The calculated band structure and density of states show that the material under load has an indirect energy band gap L→X for majority-spin direction and Г→X for the minority spin channel. The analysis charge densities show that bonding character as a mixture of covalent and ionic nature. The optical properties are analyzed and the origin of some peaks in the spectra is described. Besides, the dielectric function, refractive index and extinction coefficient for radiation up to 14 eV have also been reported.     

First principles study of electronic and optical properties of the ternary SnSb4S7 using modified Becke-Johnson potential

The electronic and optical properties of SnSb₄S₇ compound are calculated by the full-potential linearized augmented plane-wave (FP-LAPW) method. The density of states (DOS) is carried out by the modified Becke-Johnson (mBJ) exchange potential approximation based on density functional theory (DFT). The compound SnSb₄S₇ has a monoclinic structure with the space group P2₁/m with lattice parameters of a=11.331 Å, b=3.865 Å and c=13.940 Å. The band gap is calculated to be 0.8 eV. The optical parameters, like dielectric constant, refractive index, reflectivity and energy loss function were also calculated and analyzed. The present work provides information about variation of the electronic and optical properties which reveals that SnSb₄S₇ is suitable for optoelectronic devices.     

First principles study of structural,electronic and optical properties of indium gallium nitride arsenide lattice matched to gallium arsenide

First principles calculations in the framework of the full-potential linearized augmented plane wave (FP-LAPW) scheme have been carried out. The dilute-nitride zinc blende (In_xGa_1−xN_yAs_1−y) was modeled at selected nitrogen compositions of y=3.125%, 6.25% and 9.375% lattice matched to gallium arsenide (GaAs). We pay attention to the In_xGa_1−xN_yAs_1−y alloy which can be perfectly lattice matched to the GaAs over its entire compositional range. In our study, this is achieved when a condition y~2.7x is maintained. The band structure calculations were performed with and without relaxation by using the generalized gradient approximation of Engel and Vosko (EV-GGA) as well as by the modified Becke–Johnson potential exchange (TB-mBJ). The action of the localized potential of subsisted nitrogen atoms was attributed to effect of relaxation. Increasing both indium and nitrogen compositions leads to decreasing energy band gap. In addition a band anti-crossing model (BAC) was also adopted to study the composition dependence of the direct band gap of quaternary alloys, building a bridge between their electronic and linear optical properties.     

Theoretical investigation of the electronic structure,optical, elastic,hardness and thermodynamics properties of jadeite

A detailed theoretical study of the electronic structure, optical, elastic and thermodynamics properties of jadeite have been performed by means of the first principles based on the state-of-the-art of density functional theory within the generalized gradient approximation. The optimized lattice constants and the atomic positions are in good agreement with experimental data. The total density of states and partial density of states of jadeite have been discussed. The energy gap has been calculated along the Γ direction found to be 5.338 eV, which shows that jadeite has wide direct band gap. The optical properties, such as the dielectric function, refractive index, extinction coefficient, reflectivity coefficient, loss function and absorption coefficient for [100] and [001] directions have been described for the first time in the energy range 0–40 eV. The elastic constants, bulk modulus, Young׳s modulus, anisotropic factor and Poisson׳s ratio have been calculated. Furthermore, the Vickers hardness and Debye temperature of jadeite have been predicted. The calculated values of all above parameters are compared with the available experimental values.     

The effect of hydrostatic pressure on the electronic and optical properties of InP

Based on the empirical pseudo-potential method, the electronic and optical properties of the InP compound in the zinc-blende structure at ambient and under hydrostatic pressure are reported. The first-order pressure coefficients of the main band gaps (at Γ, X, and L) are given. The agreement between our calculated hydrostatic deformation potential and the available experimental data is better than 5%, whereas for the crossover pressure from direct to indirect band gap is about 10% less. The valence bandwidth increases with increasing pressure reflecting the decreased ionicity in the material of interest. Besides the electronic properties, the effect of pressure on the dielectric function is also analysed.     

First principles calculations of the electronic structure and optical properties of (001), (011) and (111) Ga0.5Al0.5As surfaces

Using the first-principles plane-wave pseudo-potential method based on density function theory (DFT), the electronic structure and optical properties of Ga_0.5Al_0.5As (001), (011) and (111) surfaces are calculated. Result shows that (001) surface is reconstructed, (011) surface is not reconstructed but wrinkled, (111) surface is only relaxed. (111) is the most stable surface. (001) surface owns the lowest work function. Absorption coefficient and reflectivity of these surfaces are smaller than bulk, the transmittance of the surfaces are larger than the bulk, which is helpful for the incident light to excite photoelectrons. The decrease of the absorption coefficient and reflectivity at (001) surface are the largest. Calculation of electronic structure and optical properties predict that the (001) surface should have the strongest photoemission.     

First-principles study of the electronic structures and optical properties of C--F--Be doped wurtzite ZnO

The electronic structure and optical properties of pure, C-doped, C-F codoped and C-F-Be cluster-doped ZnO with wurtzite structure were calculated by density functional theory with the plane-wave ultrasoft pseudopotentials method. The results indicate that p-type ZnO can be obtained by C incorporation, and the energy level of CO above valence band maximum is 0.36 eV. The ionization energy of the complex Zn16O14CF and Zn15BeO14CF can be reduced to 0.23 and 0.21 eV, individually. These results suggest that the defect complex of Zn15BeO14CF is a better candidate for p-type ZnO. To make optical properties clear, we investigated the imaginary part of the complex dielectric function of undoped and C-F-Be doped ZnO. We found that there are strong absorption in the energy region less than 2.7 eV for C-F-Be doped system comparing to pure ZnO.     

First-principles study of structural,electronic, elastic and thermal properties of intermetallic ternary compounds (RMn2Si2: R=Ce and Nd)

In this study, the structural, magnetic, electronic, elastic and thermal properties of the ternary intermetallic, RMn₂Si₂ (R=Ce and Nd), compounds are presented. The study is carried out by employing the full-potential (FP) linearized augmented plane wave (LAPW) plus local orbital (lo) approach based on the density functional theory (DFT). To depict the exchange-correlation energy (an important component of total energy calculations), the local-density approximation and the local spin density approximation (LDA/LSDA) are used. Our calculated results for equilibrium lattice parameters are in good agreement with the available experimental measurements. The total energy calculations reveal the strong dependence to the distance between atomic species in these compounds. The analysis of the partial and total densities of states (DOS) of both compounds (CeMn₂Si₂ and NdMn₂Si₂) demonstrates their metallic and magnetic character as well. Whereas the calculated values of Poisson׳s ratio and B/G present their brittle makeup. At the end, using a quasi-harmonic Debye model as implemented in GIBBS code, the thermal properties were calculated.     

Structural,electronic and optical properties of Ilmenite ATiO3(A=Fe,Co, Ni)

Ilmenite-type ATiO₃ (A=Fe, Co, Ni) crystals have been investigated via Generalized Gradient Approximation (GGA) in the scheme of Revised Perdew-Burke-Ernzerhof (RPBE) using the first-principles method. The band structures, densities of states, bond orders and charge populations, optical properties including the dielectric function ε(ω), absorption coefficient I(ω), refractive index n(ω), extinction coefficient k(ω), electron energy loss function L(ω) and reflectivity function R(ω), are calculated. The results show that the GGA-optimized geometries agree well with the experimental data. FeTiO₃ has a direct band gap, but both CoTiO₃ and NiTiO₃ exhibit indirect band gap. The analysis for densities of states and atomic charge populations exhibits that TiO bonds possess the stronger covalent bonding strength than AO bonds. The calculated optical properties along [100], [010] and [001] as well as polycrystalline directions demonstrate the significant optical anisotropy parallel and perpendicular to c-axis for ATiO₃. Finally, the origins of main peaks for optical spectra are presented based on electron transitions. Theoretical insights into the microscopic intrinsic properties of ATiO₃ should provide fundamental investigations for further understanding the Ilmenite ATiO₃ materials and improving their practical applications.     

Electronic structure,chemical bonding and optical properties of Di-2-pyrymidonium dichloride diiodide (C4H5ClIN2O) from first-principles

The electronic structure and electronic charge density of the monoclinic phase Di-2-pyrymidonium dichloride-di-iodide compound is studied by using the local density approximation (LDA) and Engel Vosko generalized gradient approximation (EVGGA). Using LDA for exchange correlation potential, we have optimized the atomic positions taken from the X-ray crystallographic data by minimization of the forces acting on the atoms. From the relaxed geometry the electronic structure, electronic charge density and the optical properties were determined. Band structures disclose that this compound has indirect energy band gap. The obtained energy band gap value using EVGGA (2.010 eV) is larger than that obtained within LDA (1.781 eV). To envision the chemical bonding nature between the composition of the investigated compound, the distribution of charge density was discussed in the (−1 0 1) crystallographic plane. The contour plot shows partial ionic and strong covalent bonding between C–O, N–C and C–H atoms. The optical properties of Di-2-pyrymidonium dichloride-di-iodide are obtained by the calculation of the dielectric function.     

First principles study of structural,electronic, elastic and magnetic properties of gadolinium hydride system GdHx (x=1, 2, 3)

The structural, electronic, elastic and magnetic properties of gadolinium and its hydrides GdH_x (x=1, 2, 3) are investigated by using Vienna ab-initio simulation package with the generalized gradient approximation parameterized by Perdew, Burke and Ernzerhof (GGA-PBE) plus a Hubbard parameter (GGA-PBE+U) in order to include the strong Coulomb correlation between localized Gd 4f electrons. At ambient pressure all the hydrides are stable in the ferromagnetic state. The calculated lattice parameters are in good agreement with the experimental results. The bulk modulus is found to decrease with the increase in the hydrogen content for the gadolinium hydrides. A pressure-induced structural phase transition is predicted to occur from cubic to hexagonal phase in GdH and GdH₂ and from hexagonal to cubic phase in GdH₃. The electronic structure reveals that mono and di-hydrides are metallic, whereas trihydride is half-metallic at normal pressure. On further increasing the pressure, a half-metallic to metallic transition is also observed in GdH₃. The calculated magnetic moment values of GdH_x (x=1, 2, 3) are in accord with the experimental values.     

Ab initio studies of structural,electronic, optical,elastic and thermal properties of Ag-chalcopyrites (AgAlX2: X=S,Se)

The ab-initio calculations for the structural, electronic, optical, elastic and thermal properties of Ag-chalcopyrites (AgAlX₂: X=S and Se) have been reported using the full potential linearized augmented plane wave (FP-LAPW) method. In this paper, the recently developed Tran–Blaha modified Becke–Johnson potential is used along with the Wu-Cohen generalized gradient approximation (WC-GGA) for the exchange-correlation potential. Results are presented for lattice constants, bulk modulus and its pressure derivative, band structures, dielectric constants and refractive indices. We have also computed the six elastic constants (C₁₁, C₁₂, C₁₃, C₃₃, C₄₄, C₆₆). The thermodynamical properties such as thermal expansion, heat capacity, Debye temperature, entropy, bulk modulus are calculated employing the quasi-harmonic Debye model at different temperatures (0–900 K) and pressures (0–8 GPa) and the silent results are interpreted. Hardness of the materials is calculated for the first time at different temperatures and pressures.     

Phase transition and related electronic and optical properties of crystalline phenanthrene: An ab initio investigation

This investigation discusses a structural phase transition of organic crystalline phenanthrene and the resulting changes of its electronic and optical properties investigated by ab initio calculations based on density functional theory (DFT). The structure of phase I has been optimized then its electronic and optical properties have been calculated. Our computational results on phase I (at ambient pressure) get along well with the available experimental data.Calculating the electronic and optical properties of phase II are proceeded in the same way and the results, particulary Raman spectra, reveal a crystallographic phase transition indicated by abrupt changes in lattice constants which are accompanied by rearrangement of the molecules. This results in modifications of the electronic structure and optical response. For both phases the band dispersion of the valence and conduction bands are anisotropic, whereas the band splitting is strongly noticeable in phase II. By calculating the imaginary part of the dielectric function of phase II, we have found the appearance of new peaks at the lowest z-polarized absorption and about 30 eV in all absorption components. Excitonic effects in the optical properties of phases I and II have been investigated by solving the Bethe–Salpeter equation (BSE) on the basis of the FPLAPW method. Phase II shows four main excitonic structures in the energy range below band gap, whereas phase I shows two. The excitonic structures in the optical spectra of phase II show a red shift in comparison to phase I. The calculated binding energies of spin-singlet excitons in phase II are larger than the ones in phase I.     

Ab-initio study of magnetic,electronic and optical properties of ZnSe doped-transition metals

The full potential linear augmented plane wave (FPLAPW) based on density-functional theory (DFT) is employed to study the electronic, magnetic and optical properties of some transition metals doped ZnSe. Calculations are carried out by varying the doped atoms. Five 3d transition elements were used as a dopant: Cr, Mn, Fe, Co and Cu in order to induce spin polarization. Our results show that, Mn and Cu-doped ZnSe could be used in spintronic devices only if additional dopants are introduced; on the contrary, transition elements showing delocalized quality such as Cr, Fe and Co doped ZnSe might be promising candidates for application in spintronics. In addition, the three materials (CrZnSe, FeZnSe and CoZnSe) are half-metallic and ferromagnetic with an important magnetic moment ranging from 3 μ_B to 4 μ_B. Furthermore, we have computed optical properties of pure ZnSe, CrZnSe, FeZnSe and CoZnSe, and found a pronounced peak occurring at low energies in all the optical curves due to TM impurity and a low difference between doped and undoped compounds for higher energies.     

A density functional study of structural,electronic and optical properties of titanium dioxide: Characterization of rutile,anatase and brookite polymorphs

Study of fundamental physical properties of titanium dioxide (TiO₂) is crucial to determine its potential for different applications, such as study of electronic band gap energy is essential to exploit it for optoelectronics and solar cell technology. We present here investigations pertaining to structural, electronic and optical properties of rutile, anatase and brookite polymorphs of TiO₂ by employing state of the art full potential (FP) linearized (L) augmented plane wave plus local orbitals (APW+lo) approach realized in WIEN2k package and framed within density functional theory (DFT). To incorporate exchange correlation(XC) energy functional/potential part into total energy, these calculations were carried out at the level of PW–LDA, PBE–GGA, WC–GGA, EV–GGA, and mBJ–GGA which are exploited as the manipulated variables in this work. From our computations, the obtained structural parameters results were found to be consistent with the available experimental results. The analysis of electronic band gap structure calculations point to TiO₂ as a semiconducting material in all three phases, whereas band gap character around Fermi level was found to be indirect for anatase, and direct for rutile and brookite phases. Density of state (DOS) profiles showed a substantial degree of hybridation between O 2p and Ti 3d in conduction and valence band regions, illustrating a strong interaction between Ti and O atoms in TiO₂ compund. In addition, our investigations of the optical properties also endorse the interband transitions from O 2p in valence band to Ti 3d in conduction band.