An Improved Study of Electronic Band Structure and Optical Parameters of X-Phosphides (X=B,Al, Ga,In) by Modified Becke-Johnson Potential

We report the electronic band structure and optical parameters of X-Phosphides (X=B, Al,Ga,In) by first-principles technique based on a new approximation known as modified Becke-Johnson (mBJ). This potential is considered more accurate in elaborating excited states properties of insulators and semiconductors as compared to LDA and GGA. The present calculated band gaps values of BP, AlP, GaP, and InP are 1.867 eV, 2.268 eV, 2.090 eV, and 1.377 eV respectively, which are in close agreement to the experimental results. The band gap values trend in this study is as: Eg (mBJ-GGA/LDA)Eg (GGA) Eg (LDA). Optical parametric quantities (dielectric constant, refractive index, reflectivity and optical conductivity) which based on the band structure are also presented and discussed. BP, AlP, GaP, and InP have strong absorption in between the energy range 4-9eV, 4-7eV, 3-7eV, and 2-7eV respectively. Static dielectric constant, static refractive index and coefficient of reflectivity at zero frequency, within mBJ-GGA, are also calculated. BP, AlP, GaP, and InP show significant optical conductivity in the range 5.2-10eV, 4.3-8eV, 3.5-7.2eV, and 3.2-8eV respectively. The present study endorses that the said compounds can be used in opto-electronic applications, for different energy ranges.     

An Improved Study of Electronic Band Structure and Optical Parameters of X-Phosphides (X=B,Al, Ga,In) by Modified Becke-Johnson Potential

We report the electronic band structure and optical parameters of X-Phosphides (X=B, Al, Ga, In) by first-principles technique based on a new approximation known as modified Becke-Johnson (mBJ). This potential is considered more accurate in elaborating excited states properties of insulators and semiconductors as compared to LDA and GGA. The present calculated band gaps values of BP, AlP, GaP, and InP are 1.867 eV, 2.268 eV, 2.090 eV, and 1.377 eV respectively, which are in close agreement to the experimental results. The band gap values trend in this study is as: E_g(mBJ-GGA/LDA) > E_g(GGA) > E_g(LDA). Optical parametric quantities (dielectric constant, refractive index, reflectivity and optical conductivity) which based on the band structure are also presented and discussed. BP, AlP, GaP, and InP have strong absorption in between the energy range 4-9 eV, 4-7 eV, 3-7 eV, and 2-7 eV respectively. Static dielectric constant, static refractive index and coefficient of reflectivity at zero frequency, within mBJ-GGA, are also calculated. BP, AlP, GaP, and InP show significant optical conductivity in the range 5.2-10 eV, 4.3-8 eV, 3.5-7.2 eV, and 3.2-8 eV respectively. The present study endorses that the said compounds can be used in opto-electronic applications, for different energy ranges.     

BaZrO3和CaZrO3能带和光学性质的第一性原理研究

采用基于密度泛函理论基础上的CASTEP软件包,计算了BaZrO3和CaZrO3的能带以及光学性质.计算得到BaZrO3直接带隙和间接带隙分别为3.49 eV和3.23eV,CaZrO3直接带隙和间接带隙分别为3.73 eV和3.38 eV.对这两种材料的介电函数、吸收系数、反射系数、折射系数、湮灭系数和能量损失系数等光学系数进行了计算,并基于电子能带对光学性质进行了解释.得出,光学特性的异同是由于其内部微观结构上的异同所引起的.     

第一性原理计算Ti掺杂CrSi2的光电特性简

采用第一性原理方法对Ti掺杂CrSi2的几何结构、电子结构、复介电函数、吸收系数、反射谱、折射率和光电导率进行了计算,对Ti置换Cr原子后的光电特性变化进行了分析.结果表明:Ti置换Cr原子后,晶格常数a,b和c均增大,体积变大;Ti的掺入引入了新的杂质能级,导致费米能级插入价带中,Cr11TiSi24变为p型半导体,带隙宽度由未掺杂时的0.38eV变为0.082eV,价带顶和导带底的态密度主要由Cr-d和Ti-d层电子贡献;与未掺杂CrSi2相比,Cr11TiSi24的介电峰发生了红移,仅在1.33eV处有一个峰,而原位于4.53eV处的峰消失;吸收系数,反射率和光电导率明显降低.     

Optical properties of InSe from 2 eV to 25 eV

The reflectivity spectrum of InSe between 2 and 25 eV is reported. From experimental results the optical functions are computed and a conduction band density of states is proposed. A comparison is made with a previous pseudopotential band structure calculation.     

Proprietes optiques de l'arsenic cristallise

The reflectivity of arsenic single crystals is measured between 0.08 and 70 eV; the optical and dielectric constants are obtained by Kramers-Kronig analysis of experimental data. The reflectivity singularities are interpreted in term of interband transitions from valence band states and from core levels. The maximum of the energy loss function is attributed to the plasma excitation of valence electrons.     

Influence of impurity hydrogen on the structure and properties of bulk Li and pressure effects

The structure and properties of a 16-atom body-centered cubic lithium cell with an interstitial hydrogen atom are studied using a pseudopotential-plane-wave method within the density functional theory at 0 K and high pressures. The host lattice is dramatically distorted by the introduction of H. Although the hydrogen atom is stable at the tetragonal site in perfect bcc host lattice, it favors the octahedral site formed by six non-equivalent Li atoms after full relaxation of the cell, showing P4/mmm symmetry within the pressures ranging from 0 to 6 GPa. The lattice ratio (a/c) changes irregularly with external pressure at about 3 GPa. The hydrogen band lies in the bottom of the valence band, separated by a gap from the metallic bands, illustrating the electronegativity of hydrogen. High reflectivity in the low frequency area induced by the impurity hydrogen is observed when only interband transitions are taken account of. A dip in reflectivity due to parallel band transitions is observed at ∼0.4 eV. Another dip at ∼4.3 eV appears when external pressure increases over 4 GPa.     

Theoretical investigation of electronic and optical properties of andalusite within density functional theory

The electronic and optical properties of andalusite were studied by using quantum-mechanical calculations based on the density functional theory (DFT). The electronic structure shows that andalusite has a direct band gap of 5.01 eV. The complex dielectric function and optical constants, such as extinction coefficient, refractive index, reflectivity and energy-loss spectrum, are calculated. The optical properties of andalusite are discussed based on the band structure calculations. It is shown that the O-2p states and Al-3s states play a major role in optical transitions as initial and final states, respectively.     

Spin-resolved unoccupied electronic band structure from quantum size oscillations in the reflectivity of slow electrons from ultrathin ferromagnetic crystals

The spin-dependent reflectivity of electrons with energies between 0 and 20 eV from Fe single crystals 2-8 monolayers thick on a W(110) surface is studied by spin-polarized low energy electron microscopy. The quantum size oscillations in the reflectivity are analyzed in a similar manner as in photoemission of ground state electrons, yielding the spin-resolved unoccupied state band structure of Fe in the Gamma N direction in the energy range studied.     

黑索金电子结构和光学性质的第一性原理研究

利用基于密度泛函理论的第一性原理方法对黑索金晶体的电子结构和光学性质进行了计算. 结果表明: 黑索金是能隙值为3.43 eV的绝缘体, 价带主要由C, N和O的2s与2p态构成, 而导带主要由N-2p和O-2p态构成; 静态介电函数ε₁(0)=1.38, 介电常数的虚部有5个峰值, 其中最大峰值在光子能量4.59 eV处, 并对造成这些峰值的可能的电子跃迁做了详细分析. 利用能带结构和态密度分析了黑索金的光反射系数、吸收系数及能量损失函数等光学性质, 发现黑索金是对光吸收、反射及能量损失不敏感的材料. 关键词： 黑索金 第一性原理 电子结构 光学性质     

畸形钙钛矿DyMnO3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广义梯度近似对畸形钙钛矿DyMnO₃的基态电子结构及光学性质进行计算和分析.结果表明优化的晶体结构参数与实验结果相符合,DyMnO₃具有非间接带隙大小为0.91 eV的能带结构,结合态密度分析了各元素价电子态的分布.计算分析包括介电常数,吸收系数,反射率等光学性质.     

Optical anisotropy of LiNbO3 and KNbO3 in the interband transition region

The reflectivity of single domain crystals of LiNbO₃ and KNbO₃ has been measured using linearly polarized light up to 10 eV. The Kramers-Kronig analysis reveals a large anisotropy of the optical constants in the interband transition region. It is shown that the large electro-optic effects observed in these compounds are due to transitions in a relatively narrow spectral region above the band edge only.     

拓扑缺陷对单壁碳纳米管电子结构及其光学光谱的影响

应用密度泛函理论计算了半导体型单壁碳纳米管(7,0)和(8,0)以及其发生镜像对称和非镜像对称Stone-Wales形变、形成异质结(7,0)—(8,0)情况下的能带结构、吸收光谱、反射光谱,并对计算结果进行了比较。研究发现： 引入拓扑缺陷态后,碳纳米管的能带结构发生了明显的变化,费米能级在不同缺陷情况下移动方向不一致;碳管的吸收和反射明显减弱且吸收峰和反射峰在低能区发生红移现象;在光子能量约为E=13 eV处各碳管的吸收谱和反射谱中均出现一特征峰,并且在引入缺陷以后该特征峰向高能区移动。文章对计算结果进行了分析和探讨,可望利用这种拓扑缺陷的引入而产生的光电特性来设计碳管光电器件。     

Fe掺杂GaN光电特性的第一性原理研究

基于密度泛函理论体系,计算了本征GaN材料和12.5%的Fe掺杂GaN体系的光电特性,分析了晶体结构、能带结构和电子态分布、介电函数、吸收系数、折射率、反射率、能量损失谱和消光系数,从理论上讨论了掺杂对体系光电特性的影响.计算所得理想GaN的禁带宽度为3.41 eV,Fe的重掺杂体系明显变窄,为3.06 eV,但仍为直接带隙半导体.本征GaN材料与Fe掺杂GaN体系的静态介电常数为5.74和6.20,折射率为2.39和2.48,能量损失最大值在20.02 eV和18.96 eV,最大吸收系数能量均在13.80 eV左右.计算结果为Fe掺杂GaN高压光电导开关材料及器件的进一步研究提供了有力的理论依据和实验支持.     

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.     

Low temperature reflectivity and optical properties of red mercury iodide

The reflectivity of red HgI₂ in the spectral range of 2–10 eV at 100 K with E⊥c is studied and the optical constants are deduced by means of the Kramers and Kronig relations. It is evidenced that the valence band is split in two subbands. Furthermore reflectivity spectra on good natural surfaces at 15 K in the two polarizations have been measured, and a high energy excitonic series, characterized by a large value of the Rydberg, is found.     

The band structure and electronic properties of sulphur nitride polymer

A semiempirical calculation of the energy band structure of (SN)_x has been made on a tight-binding model with three p orbitals per atom. An important feature is that the Fermi level crosses two overlapping conduction bands. Measurements are reported of the optical transmission spectrum between 0.2 and 4.0 eV in thin films, the free carrier reflectivity in thick films, and the hydrostatic pressure dependence of the conductivity to 15 kbar. The calculated band structure accounts for experimental results connected with interband transitions (optical absorption) and intraband effects (metallic conductivity, reflectivity, specific heat).     

Electronic structure of PbI2 from photoelectron spectra and the exciton problem

The valence band density of states for PbI₂ is determined from X-ray and u.v. induced photoelectron spectra. It is shown that the band derived from Pb 6s states is at 8 eV binding energy and not at the top of the valence bands as suggested by band structure and charge density calculations. A rigid shift in the predominantly iodine 5p derived bands to lower binding energy brings the band structure calculations into essential agreement with experiment. Pb 5d core level binding energies determined here are used to derive core level exciton energies of 0.7 eV from published reflectivity spectra.     

Zn1-xMgxO电子结构及光学性质的第一性原理GGA+U方法研究

Mg掺杂ZnO形成的固溶体Zn_1-xMg_xO（ZMO）（0 ≤ x ≤ 0.25）是一种带隙较宽、电子学性质可调控的半导体材料,在薄膜太阳电池及光电设备的透明电极等方面具有重要的应用价值。基于密度泛函理论下的第一性原理超软赝势方法,采用GGA+U计算了ZMO的电子结构和光学性质。计算结果表明,随着x值的增加,ZMO的禁带宽度由x=0时的3.32 eV增加到x=0.25时的3.78 eV;光吸收边及反射谱和能量损失谱均发生明显蓝移,峰值存在于紫外光区。计算结果与实验结论相符合。     

Electronic structure of strontium titanate

The spectra of three sets of optical functions for SrTiO₃ crystals are determined in a broad energy range of fundamental absorption. The calculations are carried out using the experimental reflectivity spectrum in the range 1–35 eV and two theoretical permittivity spectra in the ranges 0–30 eV and 0–14 eV. The special features of these spectra have been determined. The theoretical spectra of the optical functions are compared with the spectra determined using the experimental reflectivity spectrum.