Density-functional theory investigation of electronic structure,elastic properties,optical properties,and lattice dynamics of Ba_2Zn WO_6

The electronic structures,optical dielectric functions,elastic properties,and lattice dynamics of Ba2ZnWO6 have been investigated by using the generalized gradient approximation.The density of states and distributions of charge density show that O and Ba tend toward ionic bond,but O and W or Zn display the covalent bond character.The calculated energy band structure shows that Ba2ZnWO6 is a wide indirect band gap semiconductor.The static value 2.28 of the refractive index is attained.The analysis of the elastic properties of Ba2ZnWO6 indicates a rather weak elastic anisotropy.The phonon dispersion is calculated,suggesting no structural instability,which is agreement with the recent low temperature neutron diffraction experiments.The mensurability C v(phonon heat capacity) as the function of the temperature is also calculated to judge our results for future experiment.     

TiO$lt;sub$gt;2$lt;/sub$gt;纳米管电子结构和光学性质的第一性原理研究

运用基于密度泛函理论的第一性原理方法, 系统研究了小尺寸锐钛矿相(n,0)型TiO₂纳米管(D<16 Å)的几何构型、电子结构和光学性质. 结果表明: 随着管径增大, 体系单位TiO₂分子的形成能降低, 体系趋于稳定; 在管径14 Å左右, (n,0)型TiO₂纳米管会发生一次构型的转变. 能带分析显示, TiO₂纳米管的电子态比较局域化, 小管径下(D<14 Å)其导电性更好; 随着构型的转变, TiO₂纳米管由直接带隙转变为间接带隙, 并且带隙值随着管径的增大而增大, 这是由于π轨道重叠效应的影响大于量子限域效应所导致的结果. 两种效应的竞争, 使得TiO₂纳米管的介电函数虚部ε₂ (ω)谱的峰值位置随管径增大既可能红移也可能蓝移, 管径大于9 Å (即(8, 0)管)之后, TiO₂纳米管的光吸收会出现明显的增强. 关键词： 2纳米管')" href="#">TiO₂纳米管 第一性原理 电子结构 光学性质     

Refractive index,band gap energy,dielectric constant and polarizability calculations of ferroelectric Ethylenediaminium Tetrachlorozincate crystal

Single crystal of Ethylenediaminium Tetrachlorozincate has been grown by slow evaporation method. The single crystal XRD study confirms the orthorhombic structure of the crystal. The presence of functional group vibrations are ascertained through FTIR and Raman studies. In optical studies, the insulating behaviour of the material is established by Tauc plot. The refractive index and the real dielectric constant of the crystal are calculated. The electronic polarizability in the high frequency optical region is also calculated from the dielectric constant values by using the Clausius–Mossotti equation. The large value of dielectric constant is identified through dielectric studies and it points to the ferroelectric behaviour of the material. Further an experimental study confirms the ferroelectric behaviour of the material. The total polarizability of the crystal owing to the space charge, dipole, ionic and electronic polarizability contributions is obtained experimentally, and it matches well with the theoretically obtained value from Penn analysis. Further, Plasmon energy and Fermi energy of the material are also calculated using Penn analysis.     

First principle study of the structural and optoelectronic properties of cubic perovskites CsPbM3 (M=Cl, Br, I)

The highly accurate all electrons full potential linearized augmented plane wave method is used to calculate structural, electronic, and optical properties of cubic perovskites CsPbM₃ (M=Cl, Br, I). The theoretically calculated lattice constants are found to be in good agreement with the experimentally measured values. It is found that all of these compounds are wide and direct bandgap semiconductors with bandgap located at R-symmetry point, while the bandgap decreases from Cl to I. The electron densities reveal strong ionic bonding between Cs and halides but strong covalent bonding between Pb and halides. Optical properties of these compounds like real and imaginary parts of dielectric functions, refractive indices, extinction coefficients, reflectivities, optical conductivities, and absorption coefficients are also calculated. The direct bandgap nature and high absorption power of these compounds in the visible-ultraviolet energy range imply that these perovskites can be used in optical and optoelectronic devices working in this range of the spectrum.     

CuInSe2电子结构与光学性质的第一性原理计算

从头计算了CuInSe₂(CIS)体相的性质，参数设定和性质计算都基于密度泛函理论，交换相关能采用GGA，泛函形式为PBE，原子间相互作用的描述采用超软赝势.计算发现CIS中存在共价键，是一种非典型的离子型晶体，在整个晶体内存在共用电子对，Cu原子和Se原子的作用大于Se原子和In原子.CIS是一种典型的直接带隙半导体，计算得到了光学性质的各项参数，包括折射指数和反射率，吸收系数以及介电函数与光子能量的关系，发现CIS的主要光吸收峰有6个，分别为：3.1，7.6，10.0，16.1，19.0，21.0eV，理论上最强吸收峰在紫外光区.     

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.     

Enlightening the stable ferromagnetic phase of SrAO3(A= Cr,Fe and Co) compounds using spin polarized quantum mechanical approach

This is an investigation of the atomic structure, opto-electronic and magnetic properties of SrAO₃ (A = Cr, Fe and Co) compounds using first principles method. The ferromagnetic behavior is found the most stable phase for SAO. The calculated Goldschmidt's tolerance factor values predict that the studied compounds have a stable structure. Moreover, the calculated formation energy shows that SrAO₃compounds are thermodynamically stable. The calculated density of states shows that the present compounds are metal and the direction of the magnetic moments of SrCrO₃ is anti parallel to its spin. The charge density contours display a mixture of the covalent and ionic bonds between the content atoms of SrAO₃ compounds. The optical parameters are calculated using the dielectric function real and imaginary parts. From the electronic and optical properties results, beneficial industrial applications can be expected for the present compounds.     

Structural,elastic, electronic and optical properties of the cubic perovskites CaXO3 (X=Hf and Sn)

The structural, elastic, electronic and optical properties of CaXO₃ compounds with the cubic perovskites structure have been investigated, by employing a first principles method, using the plane wave pseudo potential calculations (PP-PW), based on the density functional theory (DFT), within the local density approximation (LDA). The elastic constants and their pressure dependence are calculated using the static finite strain technique. We derived the bulk, shear and Young’s moduli for ideal monocrystalline and for polycrystalline CaXO₃ aggregates which we have classified as ductile in nature. Band structures reveal that these compounds are indirect energy band gap (R-G) semiconductors; the analysis of the site and momentum projected densities, valence charge density bond length, bond population and Milliken charges, shows that bonding is of covalent–ionic nature. We have found that the elastic constants C₁₁, C₁₂, C₄₄ are in good correlation with the bonding properties. The optical constants, including the dielectric function, optical reflectivity, refractive index and electron energy loss, are calculated for radiation up to 20 eV.     

高压下c-BN的力学、电子结构及光学性质研究

为了研究不同压力下c-BN的力学性质、电子结构以及光学性质的变化,基于密度泛函理论构建了不同压力下c-BN的晶体模型。发现c-BN在不同压力下均力学稳定,随着压力增加,c-BN的弹性常数逐渐增大,材料的可压缩性逐渐变差;c-BN在零压下的禁带宽度为4.367 eV,表明c-BN是间接宽带隙半导体,随着压力增加,c-BN的禁带宽度逐渐增大,态密度谱图变化不明显;对Milliken 布居分布在不同压力下进行分析,表明随着压力增加,B、N原子杂化后形成的B-N共价性增强。对c-BN的复介电函数、折射率、反射率等进行分析,发现随着压力增大,它们都产生一定蓝移,且在整个可见光谱范围以及红外与紫外（约从204nm开始）光谱的很大范围内都透明。研究结果对高压下c-BN的应用有一定参考价值。     

Ge-Sb-Se硫系玻璃的折射率和热光系数

Ge-Sb-Se硫系玻璃被认为是极佳的红外传输材料和有潜力的非线性光学材料.在光学设计中,玻璃的线性折射率(n)及其热光系数(ζ)是关键技术参数.以预测和调控Ge-Sb-Se玻璃的n和ζ为目的,考察了玻璃的n,ζ,密度(d)和体积膨胀系数(β)与化学参数dSe和拓扑网络结构参数r的内在联系.研究发现,玻璃的n随d的增加而增大;ζ随β的增大而近似线性减小;β随dSe的减小或r的增大而减小;当Ge含量固定时, d随dSe的减小或r的增大而增大,当Sb含量固定时, d在dSe=0时具有最小值.基于实测d和n,拟合获得了Ge, Sb和Se元素在2—12μm波段的摩尔折射度(R_i),分别为R_(Ge)=10.16—10.50 cm~3/mol,RSb=16.71—17.08 cm~3/mol和RSe=11.15—11.21 cm~3/mol,根据d和R_i计算得到的n与实测值的偏差小于1%.基于实测ζ和β,拟合得到了Ge, Sb和Se元素在2—12μm波段的摩尔折射度温度系数(φ_i),分别为φ_(Ge)=21.1—22.6 ppm/K,φ_(Sb)=7.2—8.4 ppm/K和φ_(Se)=90.2—94.2 ppm/K,根据β和φ_i计算得到的ζ与实测值的偏差小于6 ppm/K.     

Insight into the structural,elastic, electronic,thermoelectric, thermodynamic and optical properties of MRhSb (M = Ti,Zr, Hf) half-Heuslers from ab initio calculations

A detailed theoretical investigation on the structural, elastic, electronic, thermoelectric, thermodynamic and optical properties of half-Heusler MRhSb (M = Ti, Zr, Hf) compounds is presented. The computations are carried out using the full potential linear augmented plane wave method (FP-LAPW) within density functional theory (DFT). The optimized lattice parameters are in fairly good agreement with available experimental data. The computed elastic constants (C_ij) and their related elastic moduli confirm the stability of the studied compounds in the cubic phase and highlight their ductile nature. Analysis of band structures and densities of states (DOS) profiles reveal the semiconducting nature with an indirect energy band gap (Γ-X). The bonding nature discussed via the electron charge density plot shows a mixture of covalent and ionic character. The evaluation of Seebeck coefficient leads to thermopower S ≥ 500 µeV which is very benefic for thermoelectric applications. Estimated thermodynamic characteristic within the quasi-harmonic approximation shows similar behavior for the three compounds. Finally, some optical spectra such as the complex dielectric function, refractive index, reflectivity, energy loss function and absorption are presented.     

First-principles calculations of nitrogen-doped antimony triselenide: A prospective material for solar cells and infrared optoelectronic devices

This study is focused on calculation of the electronic structure and optical properties of non-metal doped Sb2Se3 using the first-principles method. One and two N atoms are introduced to Sb and Se sites in a Sb₂Se₃ crystal. When one and two N atoms are introduced into the Sb₂Se₃ lattice at Sb sites, the electronic structure shows that the doping significantly modifies the bandgap of Sb₂Se₃ from 1.11 eV to 0.787 and 0.685 eV, respectively. When N atoms are introduced to Se sites, the material shows a metallic behavior. The static dielectric constants ε1(0) for Sb₁₆Se₂₄, Sb₁₅N₁Se₂₄, Sb₁₄N₂Se₂₄, Sb₁₆Se₂₃N₁, and Sb₁₆Se₂₂N₂ are 14.84, 15.54, 15.02, 18.9, and 39.29, respectively. The calculated values of the refractive index n(0) for Sb₁₆Se₂₄, Sb₁₅N₁Se₂₄, Sb₁₄N₂Se₂₄, Sb₁₆Se₂₃N₁, and Sb₁₆Se₂₂N₂ are 3.83, 3.92, 3.86, 4.33, and 6.21, respectively. The optical absorbance and optical conductivity curves of the crystal for N-doping at Sb sites show a significant redshift towards the short-wave infrared spectral region as compared to N-doping at Se sites. The modulation of the static refractive index and static dielectric constant is mainly dependent on the doping level. The optical properties and bandgap narrowing effect suggest that the N-doped Sb₂Se₃is a promising new semiconductor and can be a replacement for GaSb due to its very similar bandgap and low cost.     

The electronic and optical properties of sodalite (Na8Al6Si6O24Cl2) from first principles

This study reports the results of ab initio electronic and optical calculations for pure sodalite crystal using the linear augmented plane wave (LAPW) method within density functional theory (DFT). The calculated electronic structure revealed predominantly orbital characters of the valence band and the conduction band, and enabled us to determine the type and the value of the fundamental gap of the compound. The imaginary part of the dielectric tensor, extinction coefficient and refraction index were calculated as functions of the incident radiation wavelength. It is shown that the O 2p states and Na 3s states play the major role in optical transitions as initial and final states, respectively. The absorption spectrum is localized in the ultraviolet range between 40 and 250 nm. Furthermore, we concluded that the material does not absorb radiation in the visible range.     

Band structure and optical properties of antimony-sulfobromide: density functional calculation

The electronic structure, linear, and non-linear optical properties of ferroelectric-semiconductor SbSBr are investigated in the non-polar (paraelectric) and polar (ferroelectric) phase, using the density functional methods in the generalized gradient approximation. The electronic band structure obtained shows that SbSBr has an indirect forbidden gap of 2.16 and 2.21 eV in the paraelectric and ferroelectric phase, respectively. The linear photon-energy dependent dielectric functions and some optical functions, such as absorption and extinction coefficients, refractive index, energy-loss function, reflectivity, and optical conductivity in both phases and photon-energy dependent second-order susceptibilities in the ferroelectric phase are calculated. Moreover, some important optical parameters, such as the effective number of valence electrons and the effective optical dielectric constant, are calculated in both phases.      

Structural,elastic and optoelectronic properties of the hydrogen based perovskite compounds: Ab-initio study

The structural, elastic, electronic and optical properties of the cubic CaMH₃ (M=Ni and Pd) compounds are investigated using first principle calculations based on the density functional theory (DFT) as implemented in the Wien2k code. The calculated lattice constants are found to be in good agreement with the values reported in the previous literature. The analysis of standard enthalpy of formation shows that both CaNiH₃ and CaPdH₃ are thermodynamically stable. The bulk modulus and cohesive energy values indicate that CaNiH₃ is less compressible and more rigid than CaPdH₃. The bonding forces between atoms of the studied compounds are mainly ionic and partially covalent. The real and imaginary parts of the dielectric function are used to calculate the optical properties. The partial density of states for the present compounds are used to explain the main peaks of the optical spectra. Beneficial optoelectronic applications are predicted from the analysis of the optical spectra of CaNiH₃ and CaPdH₃ compounds.     

GaN结构相变、电子结构和光学性质

运用第一性原理平面波赝势和广义梯度近似方法,对纤锌矿结构和氯化钠结构GaN的状态方程及其在高压下的相变进行计算研究,分析相变点附近的电子态密度、能带结构和光学性质的变化机制.通过状态方程和焓相等原理得到GaN从纤锌矿到氯化钠结构的相变压强分别为43.9 Gpa和46.0 Gpa;在相变的过程中,GaN由典型的直接带隙半导体转变为间接带隙半导体材料;氯化钠结构GaN相比于纤锌矿结构,介电函数主峰值增强,本征吸收边明显往高能方向移动,氯化钠结构GaN在低能区域的光学性质差于纤锌矿结构.     

Electronic structure and optical properties of CdWO4 with oxygen vacancy studied from first principles

The electronic structures, dielectric functions and absorption coefficient of both perfect CdWO₄ crystal (CWO) and the CWO crystal containing oxygen vacancy (CWO: V _O) have been studied using the CASTEP code with the lattice structure optimized. The calculated total density of states (TDOS) of CWO: V _O indicates that the oxygen vacancy would introduce a new electronic state within the band gap compared with that of perfect CWO. The dielectric functions are calculated since the imaginary part of the dielectric function can reduce the optical absorption of a certain crystal, and then the absorption coefficient is calculated. The calculated absorption spectra show that CWO: V _O exhibits two absorption bands in the ultraviolet and visible region, peaking at about 3.0 eV (413 nm) and 3.5 eV (354 nm), respectively, which are in agreement with the experimental results showing that the yellow CWO has two optical absorption bands in this region peaking at around 350 nm and 400 nm respectively. It can be concluded that oxygen vacancy causes these two absorption bands. The calculations also indicate that the optical properties of CWO exhibit anisotropy, and can be explained by the anisotropy of the crystal lattice.     

Preparation and characterization of PbS nanoparticles in AOT micellar medium

The preparation of PbS nanoparticle is important in material science. Due to its predominant ionic character and low optical band gap (0.41 eV), it shows quantum confinement effect up to a larger size domain compared to other well studied semiconductor materials, such as ZnS and CdS, having predominantly covalent character. In this report, we present a simpler method of preparation of nanosized PbS in micellar medium of the surfactant AOT and spectrophotometric, fluorimetric, light scattering and electron microscopic characterization of the dispersion.     

掺Ge锐钛矿相TiO_2光学性质的计算

合理的掺杂是改善TiO_2活性,使其光催化性能在可见光照射下发挥作用的最有效途径之一,本文利用基于密度泛函理论的第一原理全电势线性缀加平面波方法计算掺Ge锐钛矿相TiO_2介电函数的实部、虚部和光学吸收系数.计算结果显示掺Ge锐钛矿相TiO_2介电函数虚部谱发生蓝移,与实验趋势相符;通过不用剪刀算符和固定晶格常数两方案研究掺Ge前后光谱的平移,得到蓝移是由于Ge原子替代Ti原子后晶胞体积减小造成.     

Structural stabilities, electronic, elastic and optical properties of SrTe under pressure: A first-principles study

The structural, electronic, elastic and optical properties as well as phase transition under pressure of SrTe have been systematically investigated by first-principles pesudopotential calculations. Five possible phases of SrTe have been considered. Our results show that SrTe undergoes a phase transition from NaCl-type (B1) to CsCl-type (B2) structure at 10.9 GPa with a volume collapse of 9.43%, and no further transition is found. We find that SrTe prefer h-MgO instead of wurtzite (B4) structure for its metastable phase because that the ionic compound prefers a high coordination. The elastic moduli, energy band structures, real and imaginary parts of the dielectric functions have been calculated for all considered phases, and we find that a smaller energy gap yields a larger high-frequency dielectric constant. Our calculated results are discussed and compared with the available experimental and theoretical data.