Implementation of magnesium doping in SrTiO3 for correlating electronic,structural and optical properties: A DFT study

In present work the structural, electronic and optical properties of Pure and Mg-doped SrTiO₃ perovskites are calculated via implementing density functional theory calculation. To explore these properties, ultra-soft pseudo-potential (USP) and generalized gradient approximation (GGA) is used. The inclusion of Mg at the Sr site in SrTiO₃ not only affects the electronic band structure through generating new gamma points but also band gap increases from 1.788 eV to 1.866 eV. The introduction of Mg is well explained by the partial and total density of states which is affected by incorporating dopant in pure SrTiO₃. Optical properties also affected by doping. The absorption edge shifted towards lower value from 0.37 eV to 0.06 eV as Mg-doped in the pure SrTiO₃ that represented a red shift. The refractive index increases by doping as of 2.49 to 2.52.The doping of Mg in SrTiO₃ affects positively in electronic and optical properties and makes this material a very interesting candidate for optical devices.     

Electronic properties of Pb(ZrTi)O3 solid solutions

The theoretical backgrounds and some experimental data on the electronic properties of polycrystalline Pb(Zr, Ti)O₃ solid solutions are summarized. These substances occur in the perovskite structure, and so their electronic band structure is presumed to be analogous to other perovskite compounds. Their forbidden gap energy has been determined to be about 3.30–3.56 eV on the basis of optical, photoacoustical, and photoelectrical measurements. Many local levels and traps exist in the forbidden gap because of the polycrystalline character and heterovalent doping. Their actual configurations and states strongly influence the optical, photoelectrical, piezoelectrical, and other physical properties of Pb(Zr, Ti)O₃ solid solutions.     

锰掺杂二硅化铬电子结构和光学性质的第一性原理计算

采用基于第一性原理的密度泛函理论(DFT)赝势平面波方法计算了锰掺杂二硅化铬(CrSi2)体系的能带结构、态密度和光学性件质.计算结果表明末掺杂CrSi2属于间接带隙半导体间接带隙宽度△ER=0.35 eV;Mn掺杂后费米能级进入导带,带隙变窄,且间接带隙宽度△Eg=0.24 eV,CrSi2转变为n型半导体.光学参数发生改变,静态介电常数由掺杂前的ε1(O)=32变为掺杂后的ε1(O)=58;进一步分析了掺杂对CrSi2的能带结构、态密度和光学性质的影响,为CrSi2材料掺杂改件的研究提供r理论依据.     

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.     

Intermediate band insertion by group-IIIA elements alloying in a low cost solar cell absorber CuYSe2: A first-principles study

By using first-principles calculations based on HSE06 hybrid functional, the structural, electronic, and optical properties of CuYSe₂ as a low cost absorber material have been studied. Our results show that CuYSe₂ is a semiconductor with indirect band gap of 1.46 eV and optical band gap of 2.00 eV. Especially, an intermediate band has been found in Ga and In alloyed CuYSe₂, respectively, which can be served as a stepping stone to optical absorption on low energy photons. Therefore, Ga and In alloyed CuYSe₂ with an intermediate band as a new absorber material have been proposed.     

The structural,electronic, and optical properties of organic–inorganic mixed halide perovskites CH_3NH_3Pb(I_(1-y)X_y)_3(X = Cl,Br)

Methylammmonium lead iodide perovskites(CH_3NH_3PbI_3) have received wide attention due to their superior optoelectronic properties. We performed first-principles calculations to investigate the structural, electronic, and optical properties of mixed halide perovskites CH_3NH_3Pb(I_(1-y)X_y)_3(X = Cl, Br; y = 0, 0.33, 0.67). Our results reveal the reduction of the lattice constants and dielectric constants and enhancement of band gaps with increasing doping concentration of Cl-/Br-at I-. Electronic structure calculations indicate that the valance band maximum(VBM) is mainly governed by the halide p orbitals and Pb 6 s orbitals, Pb 6 p orbitals contribute the conduction band minimum(CBM) and doping does not change the direct semiconductor material. The organic cation [CH_3NH_3]~+does not take part in the formation of the band and only one electron donates to the considered materials. The increasing trends of the band gap with Cl content from y = 0(0.793 eV) to y = 0.33(0.953 eV) then to y = 0.67(1.126 eV). The optical absorption of the considered structures in the visible spectrum range is decreased but after doping the stability of the material is improving.     

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.     

第一性原理研究B掺杂Mn_4Si_7的电子结构和光学性质

采用基于密度泛函理论的第一性原理计算方法,对未掺杂及B掺杂Mn_4Si_7的电子结构和光学性质进行理论计算.研究结果表明,未掺杂Mn_4Si_7是间接带隙半导体,其禁带宽度为0.786 eV,B掺杂后其禁带宽度下降为0.723 eV. B掺杂Mn_4Si_7是p型半导体材料.未掺杂Mn_4Si_7在近红外区的吸收系数达到10~5 cm~(-1),B掺杂引起Mn_4Si_7的折射率、吸收系数、反射系数及光电导率增加.     

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.     

Electronic structure,optical dielectric constant and born effective charge of EuAlO3

EuAlO₃ (EAO) is synthesized by the sol–gel process. The Rietveld refinement of the X-ray diffraction data shows that the material has orthorhombic structure with Pbnm space group. The density functional theory calculations are initiated with the experimental lattice parameters. The full potential linearized augmented plane wave method and projector augmented wave method are used to investigate the ground state properties of EAO. An indirect band gap of 1.8 eV is observed with the valence band maximum at the Γ point and the conduction band minimum at the R point. The X-ray photoemission spectroscopy (XPS) spectra of EAO are obtained in the energy window of 0–1000 eV. Using the electronic density of states, the valence band (VB) spectrum of EAO is generated and compared with the observed VB-XPS spectrum. The optical dielectric constant and the refractive index of the material are calculated for the photon energy radiation. The optical properties show a considerable anisotropy in the material. The Born effective charge of various elements and the dielectric tensor of EAO have been calculated.     

掺稀土元素(Y，La)的γ-Si3N4的电子结构和光学性质

采用基于密度泛函的平面赝势方法(PWP)和广义梯度近似(GGA)，计算了未掺杂和掺杂稀土(Y，La)的γ-Si₃N₄中N-Y(La)键的布居值和它们的键长、掺杂后能带结构和态密度.发现掺杂后的带隙要减小，并且可能形成新的半导体，这将为找到新的半导体提供一个方向.还进一步研究了掺杂稀土(Y，La)后的光学性质，掺杂后有更高的静态介电常数，可以作为新的介电材料和好的折射材料，这对于一定的光学元件有潜在的应用前景.     

过渡金属(Ni)掺杂ZnV2O4的第一性原理计算

采用基于密度泛函理论下的MS软件模拟了过渡金属Ni掺杂ZnV₂O₄前后的能带结构、态密度以及光学性质.结果表明：ZnV₂O₄具有间接的光学跃迁且能带间隙为0.355 eV,Ni掺杂后能带间隙增加为0.785 eV,且带隙类型不变,引入的Ni-3d轨道电子对ZnV₂O₄的价带和导带组成提供了较大贡献.光学性质结果表明ZnV₂O₄为一种低介电材料,在可见光区的吸收系数和折射率较低,主要表现为紫外吸收.掺杂Ni后,在可见光区的吸收特性和光电导率均增大,有效改善了ZnV₂O₄在可见光区的光电性能.     

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.     

Mn掺杂6H-SiC的第一性原理研究

本文通过密度泛函理论第一性原理平面波超软赝势计算方法计算了Mn掺杂6H-SiC的电子结构与光学性质。计算结果显示掺杂Mn后的6H-SiC为间接带隙p型半导体,且带隙较本征体有所降低,带隙由2.022 eV降为0.602 eV,电子从价带跃迁所需能量减少。掺杂后的Mn的3d能级在能带结构中以杂质能级出现,提高了载流子浓度,导电性增强。光学性质研究中,掺杂Mn后的介电函数虚部在低能处增加,电子激发态数量增多,跃迁概率增大。掺杂后的光吸收谱能量初值也较未掺杂的3.1 eV扩展到0 eV,反射谱发生红移。由于禁带宽度的降低使得光电导率起始范围得到扩展。     

First-principles investigation of electronic and optical properties in wurtzite Zn<Subscript>1-x</Subscript>Mg<Subscript>x</Subscript>O

A first-principles study has been performed to evaluate the electronic and optical properties of wurtzite Zn_1-xMg_xO. Substitutional doping is considered with Mg concentrations of x = 0, 0.0625, 0.125, 0.1875 and 0.25, respectively. Mg incorporation can induce band gap widening due to the decrease of Zn 4s states. The imaginary part of the dielectric function shows that the optical transition from band edge emission decreases slightly with increasing Mg contents. The optical band gap also increases from 3.2 to 3.7 eV with increasing Mg contents from 0.0625 to 0.25. The calculated results suggest that relatively high Mg concentration is necessary for effective band gap engineering of wurtzite Zn_1-xMg_xO.     

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.     

Structural,electronic and optical properties of cubic fluoroelpasolite Cs2NaYF6 by density functional theory

First-principles full-potential linearized augmented plane-wave method based on density functional theory is used to investigate the structural, electronic and optical properties of the cubic fluoroelpasolites Cs₂NaYF₆ within the local density approximation (LDA) and generalized gradient approximation (GGA) for potential exchange correlation. The modified Becke–Johnson (mBJ) potential approximation is also used for calculating the electronic and optical properties of the material. We have analyzed the structural parameters, total and partial densities of states, dielectric functions, absorption and reflectivity. The results show that the band structure of the fluoroelpasolites Cs₂NaYF₆ has an insulating behavior for the two directions of spin and as a result there is no net magnetic moment. A wide band gap of 9.6 eV is obtained with mBJ-GGA, which allows the application of this material as X-ray storage phosphor materials and scintillators.     

Effect of Nb doping on morphology,crystal structure,optical band gap energy of TiO2 thin films

Nb–TiO₂ nanofibers and thin films were prepared using a sol–gel derived electrospinning and spin coating, respectively, by varying the Nb/Ti molar ratios from 0 to 0.59 to investigate the effect of Nb doping on morphology, crystal structure, and optical band gap energy of Nb–TiO₂. XRD results indicated that Nb–TiO₂ is composed of anatase and rutile phases as a function of Nb/Ti molar ratio. As the Nb/Ti molar ratio rose, the anatase to rutile phase transformation and the reduction in crystallite size occurred. The band gap energy of Nb–TiO₂ was changed from 3.25 eV to 2.87 eV when the anatase phase was transformed to rutile phase with increasing the Nb doping. Experimental results indicated that the Nb doping was mainly attributed to the morphology, the crystal structure, the optical band gap energy of Nb–TiO₂, and the photocatalytic degradation of methylene blue.     

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.     

First-principles study on the electronic and optical properties of BiFeO3

The structural, electronic, and optical properties of multiferroic bismuth ferrite (BiFeO₃) are investigated using density functional theory within generalized gradient approximation (GGA). The calculated lattice parameters are in good agreement with the experimental data. The electronic structure shows that BiFeO₃ has an indirect (very close to direct) band gap of 1.06 eV. The complex dielectric function, absorption spectra, refractive index, extinction coefficient, energy-loss spectrum and reflectivity are calculated, and the results are compared with the available experimental data. Finally, the optical properties of BiFeO₃ are discussed based on the band structure calculations.