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     

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.     

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.     

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.     

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。     

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.     

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.     

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.     

The under-pressure behaviour of mechanical,electronic and optical properties of calcium titanate and its ground state thermoelectric response

Abstract

In this study, the elastic, electronic, optical and thermoelectric properties of CaTiO₃ perovskite oxide have been investigated using first-principles calculations. The generalised gradient approximation (GGA) has been employed for evaluating structural and elastic properties, while the modified Becke Johnson functional is used for studying the optical response of this compound. In addition to ground state physical properties, we also investigate the effects of pressure (0, 30, 60, 90 and 120 GPa) on the electronic structure of CaTiO₃. The application of pressure from 0 to 90 GPa shows that the indirect band gap (Γ-M) of CaTiO₃ increases with increasing pressure and at 120 GPa it spontaneously decreases transforming cubic CaTiO₃ to a direct (Γ-Γ) band gap material. The complex dielectric function and some optical parameters are also investigated under the application of pressures. All the calculated optical properties have been found to exhibit a shift to the higher energies with the increase of applied pressure suggesting potential optoelectronic device applications of CaTiO₃. The thermoelectric properties of CaTiO₃ have been computed at 0 GPa in terms of electrical conductivity, thermal conductivity and Seebeck coefficient.     

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.      

Ni掺杂对Cu团簇结构稳定性的影响

采用密度泛函理论对Cu_n和Cu_n-1Ni(n=3-14)团簇的结构及稳定性进行研究.结果证明Cu_n(n=3-14)团簇的基态不是密实结构而是类似双平面的构型;计算表明:Ni掺杂增加了铜团簇的稳定性,Cu_nNi(n=2-13)团簇的最稳态结构与单质铜团簇不同而是以形成二十面体为基础的密实结构,Ni原子趋于和尽量多的Cu原子成键而最终陷入笼状团簇的中心;偶数个粒子的团簇具有相对高的稳定性,尤其Cu₃Ni,Cu₇Ni和Cu₉Ni;陷入笼状团簇内部的Ni原子带正电,使得位于表面的Cu原子带负电,从而增加了由这种团簇构成的材料的化学稳定性,如耐腐蚀性等.     

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.     

Elastic,electronic structure,and optical properties of orthorhombic Na<Subscript>3</Subscript>AlF<Subscript>6</Subscript>: a first-principles study

First-principles investigation of elastic, electronic, and optical properties of orthorhombic Na₃AlF₆ has been carried out by DFT using plane-wave pseudo-potentials within the LDA and GGA. Calculated lattice parameters agree well with experimental results. From calculated elastic constants, Na₃AlF₆ is a mechanically stable anisotropic and behaves in a ductile manner. Electronic structure analysis indicates that Na₃AlF₆ behaves as an insulator with a direct band gap of 6.065 eV in LDA and 5.868–5.949 eV in GGA. DOS, population analysis, and charge densities difference indicate that Al-F bonds are mainly ionic as well as partially covalent due to the hybridization of F-2p and Al-3s (3p) states. Moreover, the imaginary part of calculated dielectric function ε₂(ω) shows three prominent peaks due to the inter band transitions F 2p states→Na 3s states. From calculated ε (ω), other optical properties such as reflectivity and refractive index are also obtained up to the photon energy range of 40 eV.     

稀土Gd掺杂新型二维材料磷烯改性研究

本文采用第一性原理赝势平面波法, 计算并分析了稀土Gd掺杂磷烯的物理结构、电子结构、磁性以及光学性质. 计算表明: 在掺杂原子Gd附近引起了磷烯物理结构上的变化. 能带数量明显增多变密, 带隙变窄由0.921eV变为0.578eV. 同时, 由于Gd原子的4f和5d轨道电子两种自旋取向分布具有不对称性, 给体系引入了强磁性, 计算得到的自旋磁矩为7.470B. 磷烯材料的复介电函数是各向异性的, 同时可以得出磷烯材料在其它光学性质方面也是各向异性的. Gd掺杂后使材料的介电性能增强. 在紫外光的能量范围内, 不同极化方向上的反射率和损失函数的峰值降低, 说明Gd的掺入使材料对紫外光的敏感度有所减弱. 希望以上研究结果能为新型二维材料磷烯在光电和稀磁半导体材料的设计与开发方面提供理论依据.     

ZnO电子结构与光学性质的第一性原理计算

计算了ZnO电子结构和光学线性响应函数,从理论上给出了ZnO材料电子结构与光学性质的关系。所有计算都是基于密度泛函理论框架下的第一性原理平面波超软赝势方法。利用精确计算的能带结构和态密度分析了带间跃迁占主导地位的ZnO材料的介电函数、反射谱、反射率以及消光率,理论结果与实验符合甚佳,为ZnO光电材料的设计与应用提供了理论依据。同时,计算结果也为精确监测和控制ZnO材料的生长过程提供了可能性。     

T型石墨烯及其衍生物的结构与电子特性

采用基于密度泛函理论的第一原理方法研究了T型石墨烯及其衍生物-n(n=1—5)的结构稳定性和电子结构性质.T型石墨烯是一种拥有四角形环的二维碳材料同素异构体,通过改变连接四角形环的碳链上的碳原子个数n,可以得到一系列的sp-sp~2杂化结构,称其为T型石墨烯衍生物-n.计算结果表明:这些材料的结构稳定性、化学键类型和电子结构性质都依存于n的奇偶性.其中T型石墨烯(n=0)的结构最稳定,并形成一个由8个碳原子构成的大环.声子谱计算的结果表明,n为偶数时的体系具有动力学稳定性,而n为奇数时的体系则是不稳定的.n为偶数时体系四角形环之间的碳链上的化学键呈单、三键交叉排列,体系显示为金属性特征,且随着n的增大,体系的金属性加强.n为奇数时体系四角形环之间的碳链上的化学键则为双键连续排列,体系呈金属性且具有磁性(n=1除外).研究表明该系列材料作为一种新的二维碳材料同素异构体,具有独特的结构和丰富的电子结构特性,很可能在纳米器件中得到广泛应用.     

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.