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.     

Selenium alloying of indium sulfide: Ab-initio study of structural,electronic and optical features

In the framework of density functional calculations and using the Linear Augmented Plane Waves with local orbital method (LAPW+lo), we have investigated the structural, electronic and optical properties of indium sulfoselenide (InS_1−xSe_x). The present study confirms that InS_1−xSe_x are indirect band gap materials. The non-linear dependence concentration x of the theoretical forbidden energy band is clearly visible and the microscopic origins of gap bowing are identified and calculated. In order to identify the angular momentum characteristics of the bands structure, the total and partial densities of states (DOS and PDOS) are analyzed. The feature bonding is also investigated from charge density study. Using the projected total densities of states (DOS) and the bands structure, we have calculated the linear optical properties, namely, the complex dielectric function ε(ω), refractive index n(ω), absorption coefficient α(ω) and the electron energy loss L(ω). In particular, we take into account the effect of Se composition on anisotropy, real part of the dielectric function and refractive index. The present alloy is found to be a challenging material in optoelectronic, medical and photovoltaic devices. Good agreements are found with the available experimental and theoretical results.     

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 the electronic structures and magnetic properties of transition metal-doped cubic indium nitride

First principles density functional calculations, using a full potential linearized augmented plane wave (FP-LAPW) method in local spin density approximation(LSDA), have been performed in order to investigate the structural, electronic and magnetic properties of In_1−xTM_xN(TM=Cr,Fe,Mn,V) in zinc-blende phase. Dependence of structural parameter values on the composition x have been analyzed in the x=0.25, x=0.50, and x=0.75, we found the existence of deviation from Vegard׳s law. Calculated electronic structure and the density of states of these alloys are discussed in terms of the contribution of TM 3d, N 2p, and In 3d states. The magnetic moment of In_1−xTM_xN has been studied by increasing the concentration of TM atom. The contribution of TM atom is the most important source of the total magnetic moment in these alloys, while it is minor in In and N.     

Structural,chemical bonding and optoelectronic properties of Mg doped zinc chalcogenides: A first principles study

A first-principal technique is employed to investigate the concentration dependence of the structural, electronic band structure, optical and chemical bonding properties of Zn_1−xMg_xS, Zn_1−xMg_xSe and Zn_1−xMg_xTe alloys. Structural parameters such as lattice constants and bulk moduli are found to vary non-linearly with changing concentration x and deviating from Vegard׳s law. Parent binaries as well as ternary alloys have a direct band gap (Γ–Γ) which increases non-linearly with increment in concentration. Chemical bonding nature changes from strong covalency to partial ionic character in increasing Mg-contents. The direct band gap and high optical activity in visible and ultraviolet range reveal the implication of these alloys in the optoelectronic devices applications.     

Structural,elastic, electronic and thermodynamic properties of uranium filled skutterudites UFe4P12: First principle method

We present a theoretical study of structural, elastic, thermodynamic, and electronic properties of the uranium filled skutterudite UFe₄P₁₂. We use the full-potential linear muffin–tin orbital (FP-LMTO) method in which the local density approximation (LDA) is used for the exchange-correlation (XC) potential. The lattice parameter at equilibrium, the bulk modulus, its pressure derivative, the elastic constants and the band structure energy of the filled skutterudite UFe₄P₁₂ are calculated and systematically compared to available theoretical and experimental data. Herein, we use the total energy variation as function of strain technique to determine independent elastic constants and their pressure dependence. Furthermore, using quasi-harmonic Debye model with phonon effects, the effect of pressure P and temperature T on the lattice parameter, bulk modulus, thermal expansion coefficient, Debye temperature and the heat capacity of UFe₄P₁₂ are investigated for the first time. Band structure of UFe₄P₁₂ indicates a tendency of forming a pseudo-gap that appears above the Fermi level at Γ point. This is a unique characteristic of skutterudite, especially when a single phosphorous p-band crosses the Fermi level. The crossing band is, indeed, pushed down by the repulsion of U f-resonance states.     

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 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.     

Se和Cd掺杂GaN电子结构与光学性质的第一性原理研究

基于密度泛函理论的第一性原理,使用GGA+U方法分别计算Se和Cd单掺与共掺杂GaN体系的晶格常数、电子结构及光学性质.结果表明:与本征GaN相比,掺杂后体系的晶格常数发生了改变,禁带宽度减小,吸收光谱均发生红移,表明掺杂使体系的光谱响应范围得到更大拓展.其中,Cd单掺GaN体系的禁带宽度最小,并在费米能级附近有杂质能...     

First principles calculations of structural,electronic and optical properties of zinc aluminum oxide

A first principles study of structural, electronic and optical properties of zinc aluminum oxide (ZnAl₂O₄) by means of the full potential linear augmented plane wave method is presented. The local density approximation is used for the exchange-correlation potential. A direct band gap of 4.19 eV, in agreement with experiment (E_g=3.9 eV), was determined. ZnAl₂O₄ is transparent in the visible spectral region; the excitonic transition associated with the fundamental band gap is 4.17 eV. The refractive index value is 1.74 in the ultraviolet spectral region.     

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.     

First principle studies of structural, elastic, electronic and optical properties of Zn-chalcogenides under pressure

Structural, elastic, electronic and optical properties ofzinc-chalcogenides （viz. ZnX, X = S, Se and Te） are studied in zinc-blende structure under hydrostatic pressure using the full-potential linearized augmented plane wave method. Generalized gradient approximation is used for exchange correlation potentials. Pressure-dependent lattice constants and bulk moduli are obtained using the optimization method. Young＇s modulus, Poisson＇s ratio, internal strain parameter and anisotropy are also calculated. The higher values of Young＇s modulus in comparison to the bulk modulus show that these materials are hard to break. Poisson＇s ratio is computed for the first time for these materials to the best of our knowledge and its values show higher ionic contribution in these materials. Modified Becke and Johnson （mBJ） method is used to study band gaps, density of states, dielectric function and refractive index. Electronic study shows direct band gaps convert to indirect band gaps with increasing pressure in the case of ZnS and ZnTe. We compared our results with other theoretical and experimental results. Our results are far better than other theoretical results because mBJ is the best technique to treat Ⅱ-Ⅵ semiconductors.     

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.     

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.     

Structural,morphological, optical,and magnetic properties of Ni-doped CuO nanostructures prepared by a rapid microwave combustion method

In the present paper, we report a facile and rapid microwave-assisted combustion synthesis method for the preparation of pure and Ni-doped CuO nanostructures with different weight ratios (0.5, 1.0, 1.5, and 2.0 at wt% of Ni). The structure and morphology of the pure and Ni-doped CuO samples were investigated by X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), energy dispersive x-ray analysis (EDX), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy and vibrating sample magnetometry (VSM). XRD patterns refined by the Rietveld method indicated the formation of single-phase monoclinic structure and also confirmed that Ni ions are successfully doped into CuO crystal lattice by occupying Cu ionic sites. Interestingly, the morphology was found to transform substantially from nanoflowers to nanoparticles with close-packed periodic array, and then into nanocrystals with the variation of Ni content. The optical band gap estimated using DRS was found to be 3.9 eV for pure CuO and then increases up to 4.3 eV with increasing Ni content. PL spectra at room temperature showed a strong green emission band, and thereby confirmed the above results. Magnetic measurements reveal a room temperature ferromagnetism (RTFM) with an optimum value of saturation magnetization of 1.3140×10⁻³ emu/g for 2.0 wt% of Ni.     

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.