First-principle study of electronic structure and optical properties of 3C-BC4N

The 3C-BC₄N, as a kind of superhard material with many potential practical applications, is studied using first-principle calculations, evaluating the structural parameters, charge transfers, bond populations, band structures, density of states, and optical properties. All the calculations are performed after geometric optimization starting from a six-atom, trigonal, and unit-cell structure. The results indicate the following: all the configurations are metastable; the band gap of five configurations of 3C-BC₄N is highly dependent on the atomic arrangement; BC₄N-1 exhibits insulating behavior; BC₄N-3 exhibits semiconductor or semimetallic behavior, while BC₄N-2, BC₄N-4, and BC₄N-5 exhibit metallic behavior; and all the configurations are transparent in the visible light region.     

Mn掺杂Fe2B晶体结构、力学性能及电子结构的第一性原理研究

基于密度泛函理论的第一性原理计算方法,本文系统地研究了Fe8-xMnxB4 (x = 0, 0.25, 0.5, 1, 2, 3, 4, 5, 6, 7 ,8)的晶体结构、机械性能和电子结构。计算得到Fe2B的晶格常数与实验值相符,所有相都具有良好的热力学稳定性和机械稳定性。随着Mn掺杂浓度逐渐增大,Fe8-xMnxB4的各向异性先减弱后增强,Fe7.75Mn0.25B4的各向异性最弱。当Mn掺杂浓度较低时,Fe8-xMnxB4的硬度略微降低,韧性增强。除了Fe7Mn1B4、Fe6Mn2B4、Fe5Mn3B4、Fe4Mn4B4之外,其余的Fe8-xMnxB4相的韧性均比Fe2B好。由电子结构可以发现,Fe8-xMnxB4的力学性能主要由Fe-B键或Mn-B键决定。Mn掺杂到Fe2B中会使得B-B共价键增强,Fe2B的本征脆性得到改善,同时Fe2B的磁性不断减弱。     

First-principle study of the electronic and optical properties of BInGaAs quaternary alloy lattice-matched to GaAs

The first-principle calculations based on density functional theory have been used to study the electronic and optical properties of zinc-blende BInGaAs quaternary alloy lattice-matched to GaAs. The calculated results show the band gap of BInGaAs alloy are direct and the band gap will reduce with the increment of boron and indium composition. The electronic structures of BInGaAs alloy are analyzed via the calculation of density of states. The variation of optical properties including dielectric function, absorption coefficient, reflectivity, refractive index and energy loss function of the alloy were also investigated in detail.     

The electronic and optical properties of Cu doped CdI2

Based on the density functional pseudopotential method, the electronic structures and the optical properties of CdI₂ doped with Cu are investigated in detail. The calculation results indicate that the defect of Cu(Cd) exists steadily with a certain solubility. For the Cu doped CdI₂, the new highly localized impurity bands induced by Cu 3d states lie just across the Fermi energy at the top of the valence band. The doping of Cu induces reduction of band gap of CdI₂; red shifts are revealed in both the imaginary part of dielectric function and the absorption spectra corresponding to the change in band gaps. Moreover, the study of the reflection spectrum and the loss function shows that the doped Cu is responsible for the increased reflection peak intensity and the red shift of the plasma resonant frequency of CdI₂.     

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.     

First-principle calculations of structural,electronic and magnetic investigations of Mn2RuGe1-xSnx quaternary Heusler alloys

First-principles calculations were used to calculate the structural, electronic and half-metallic ferromagnetism of Mn₂RuGe_1-xSn_x (x?=?0, 0.25, 0.50, 0.75, 1) Heusler alloys. The Hg₂CuTi-type structure is found to be energetic more than Cu₂MnAl-type structure for both Mn₂RuGe and Mn₂RuSn compounds. The calculated lattice constants for Mn₂RuGe and Mn₂RuSn are 5.91?Å and 6.17?Å, respectively. The electronic band structures and density of states of Mn₂RuGe show a half metallic character with total magnetic moments, 2 μ_B per formula unit that are in good agreement with Slater-Pauling rule with indirect band gap, 0.31?eV along the direction Γ –X. It is observed that the total magnetic moment per cell increases as Sn concentration increases in the Heusler alloys.     

First-principle study of electronic structure and stability of Sn0.5Sb0.5O2

A theoretical study on Sb-doped SnO₂ has been carried out by means of periodic density functional theory (DFT) at generalized gradient approximation (GGA) level. Stability and conductivity analyses were performed based on the formation energy and electronic structures. The results show that Sn_0.5Sb_0.5O₂ solid solution is stable because the formation energy of Sn_0.5Sb_0.5O₂ is −0.06 eV. The calculated energy band structure and density of states showed that the band gap of SnO₂ narrowed due to the presence of the Sb impurity energy levels in the bottom of the conduction band, namely there is Sb 5s distribution of electronic states from the Fermi level to the bottom of conduction band after the doping of antimony. The studies provide a theoretical basis to the development and application of Sn_1−xSb_xO₂ solid solution electrode.     

Electronic and optical properties of kesterite Cu2ZnSnS4 under in-plane biaxial strains: First-principles calculations

The electronic structures and optical properties of Cu₂ZnSnS₄ (CZTS) under in-plane biaxial strain were systematically investigated using first-principles calculations based on generalized gradient approximation and hybrid functional method, respectively. It is found that the fundamental bandgap at the Γ point decreases linearly with increasing tensile biaxial strain perpendicular to c-axis. However, a bandgap maximum occurs as the compressive biaxial strain is 1.5%. Further increase of compressive strain decreases the bandgap. In addition, the optical properties of CZTS under biaxial strain are also calculated, and the variation trend of optical bandgap with biaxial strain is consistent with the fundamental bandgap.     

Concentration-dependent electronic structure and optical absorption properties of B-doped anatase TiO2

The concentration-dependent electronic structures and optical properties of B-doped anatase TiO₂ have been calculated using the density functional theory. The calculated results indicate that the electronic structures of B-doped TiO₂ have changed compared with those of pure TiO₂, which is mainly due to the new midgap states induced by B doping. As to the optical properties, we calculate the imaginary part of dielectric function ε₂(ω) and optical absorption spectra of pure and B-doped TiO₂. Two transitions E₁ and E₂ emerged after B doping. The intensity of absorption is enhanced by B doping both in the UV and visible regions. According to the results of imaginary part of dielectric function ε₂(ω) and DOS, it can be concluded that the two optical transitions correspond to the transitions from the O 2p states in the top of valence band to the midgap states and from the midgap states to the Ti 3d states in the bottom of conduction band, respectively. These results have important implications for the further development of photocatalytic materials.     

Theoretical studies on the electronic structure and magnetic properties of Cu(2,5-dmpz)Cl2

First-principles calculations have been performed to study the electronic structure, the metallic and magnetic properties of Cu(2,5-dmpz)Cl₂. The calculations are based on the density functional theory (DFT) with the generalized gradient approximation (GGA) and the full-potential-linearized-augmented plane wave (FPLAPW) method. The total energy, magnetic moment, density of states (DOS) and electronic band structure are calculated. The results reveal that the compound has a stable semiconductive antiferromagnetic (AFM) ground state and a semiconductive ferromagnetic (FM) metastable state, which is in good agreement with the experimental results. Based on the spin distribution and the DOS, it is found that the spin magnetic moment is mainly from the Cu²⁺, and with relative small contribution from Cl, N atoms.     

Ab initio study of structural, electronic and optical properties of MnHg(SCN)4 and FeHg(SCN)4

 The structural, electronic and optical properties of MnHg(SCN)₄ and FeHg(SCN)₄ were studied by means of quantum-mechanical calculations based on the density-functional theory and pseudopotential method. The lattice constants can be compared with the experimental values when the effects of temperature are considered. The peaks of partial density of states of S, C, N and Hg of FeHg(SCN)₄ have a tendency of shifting to the higher energy levels relative to those of MnHg(SCN)₄. The distributions of the 3d electronic states in the transition metal atoms show quite large difference and decide different optical properties. We found that absorptional peaks of FeHg(SCN)₄ lag behind those of MnHg(SCN)₄ and the peak in the infrared range has a higher absorptional intensity, which are in accord with the experimental results. By analyzing the distributions and transitions of the 3d electronic states, we explained the different absorption phenomena.     

First-principle calculations on optical properties of C-N-doped and C-N-codoped anatase TiO2

The electronic structures, dipole moment and optical properties of C-N-doped and C-N-codoped anatase titanium dioxide (TiO₂) are studied using the plane-wave ultrasoft pseudopotential method of density functional theory (DFT). The results revealed that the absorption coefficients of pure TiO₂ and N-doped TiO₂ are consistent with experimental values in the visible-light region. The bands originating from C/N-2p states lie in the band gap of doped TiO₂. A visible-light absorption edge red-shift can be observed. The atomic charges have changed, resulting in devation of the center of gravity of the negative electric charge from the positive electric charge in the super-cell, and their dipole moment would not be zero. The dipole moment has large influence on the optical responses in the visible region of TiO₂. Because of the small distance (0.531 nm) between C and N atoms, the covalent bond component was easily enhanced between C atom and adjacent O atom, the covalent bonds making it more difficult for the carrier transfer. Moreover, its optical absorption coefficient is going to reduce in the visible-light region. Under the condition of the larger distance (0.691 nm) between C and N atoms, their interaction can be reduced, which is beneficial to electrons transition; as a result, a significant improvement of the photocatalytic activity of TiO₂ has been found under the visible-light irradiation.     

First-principles study of electronic and optical properties of N-doped SrHfO3

The plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT) is used to investigate the doping effect of N substituting for O in cubic SrHfO₃. The calculated results show that the reaction from pure elements to final compounds is favorable and the final compounds are energetically stable. Electronic structure analysis shows the band gaps narrowing with the increase of N concentration due to the presence of the impurity state of N 2p on the top of the valence band and the acceptor energy levels above the Fermi energy, which may be responsible for the red-shift. Besides, the optical absorption edge has been gradually red shifted with increasing N concentration.     

Effect of environment and heat treatment on the optical properties of RF-sputtered SnO2 thin films

Thin films of SnO₂ were deposited by RF-magnetron sputtering on quartz substrates at room temperature in an environment of Ar and O₂. The XRD pattern shows amorphous nature of the as-deposited films. The optical properties were studied using the reflectance and transmittance spectra. The estimated optical band gap (E_g) values increase from 4.15 to 4.3 eV as the Ar gas content decreases in the process gas environment. The refractive index exhibits an oscillatory behavior that is strongly dependent on the sputtering gas environment. The Urbach energy is found to decrease with increase in band gap. The band gap is found to decrease on annealing the film. The role of oxygen defects is explored in explaining the variation of optical parameters.     

Ab initio study of the structural,electronic, elastic and magnetic properties of Cu2GdIn,Ag2GdIn and Au2GdIn

We preformed first-principle calculations for the structural, electronic, elastic and magnetic properties of Cu₂GdIn, Ag₂GdIn and Au₂GdIn using the full-potential linearized augmented plane wave (FP-LAPW) scheme within the generalized gradient approximation by Wu and Cohen (GGA-WC), GGA+U, the local spin density approximation (LSDA) and LSDA+U. The lattice parameters, the bulk modulus and its pressure derivative and the elastic constants were determined. Also, we present the band structures and the densities of states. The electronic structures of the ferromagnetic configuration for Heusler compounds (X₂GdIn) have a metallic character. The magnetic moments were mostly contributed by the rare-earth Gd 4f ion.     

First-principles study of the structural, elastic, electronic and optical properties of the monoclinic BiScO3

The structural, elastic, electronic and optical properties of the monoclinic BiScO₃ are investigated in the framework of the density functional theory. The calculated structural parameters are in agreement with the experimental values. Moreover, the structural stability of BiScO₃ system has been confirmed by the calculated elastic constants. The band structure, density of states, charge transfers and bond populations are also given. The results indicate that BiScO₃ has a direct band gap of 3.36 eV between the occupied O 2p states and unoccupied Bi 6p states, and its bonding behavior is a combination of covalent and ionic nature. Finally, the absorption spectrum, refractive index, extinction coefficient, reflectivity, energy-loss function and dielectric function of the monoclinic BiScO₃ are calculated. In addition, the variation of the static dielectric constants ε₁(0) as a function of pressure for BiScO₃ is also discussed.     

Electronic and optical properties of CuGaS2: First-principles calculations

Electronic structure and optical properties of CuGaS₂ are calculated using the full potential linearized augmented plane wave plus local orbitals method. The calculated equilibrium lattice is in reasonable agreement with the experimental data. The electronic structures indicate that CuGaS₂ is a semiconductor with a direct bandgap of 0.81802 eV. Furthermore, other experiments and theory also show that this material has a direct bandgap. It is noted that there is quite strong hybridization between Ga 3d and S 3s orbitals, which belongs to the (GaS₂)⁻. The complex dielectric functions are calculated, which are in good agreement with the available experimental results.     

第一性原理研究Fe掺杂SnO2材料的光电性质

采用基于第一性原理的线性缀加平面波(FP-LAPW)方法,研究Fe掺杂SnO₂材料电子结构和光学性质,包括电子态密度、能带结构、介电函数和其他一些光学图谱. 研究结果表明,掺Fe后材料均属于直接跃迁半导体,且呈现半金属性;随掺杂浓度增加,费米能级进入价带,带隙逐渐减小,Fe原子之间耦合作用增强;通过掺杂能够在一定程度上改变成键性质,使其具有金属键性质. 光学谱线(吸收谱、消光系数等)与介电函数虚部谱线相对应,均发生蓝移,各峰值与电子跃迁吸收有关,从理论上指出光学性质和电子结构的内在联系. 关键词： 能带结构 态密度 光学性质 介电函数     

Cr和C共掺TiO_2的电子结构和光学性质的研究

利用第一性原理计算,研究了Cr与C共掺锐钛矿型TiO_2的能带的结构,态密度和光学性质.我们构建了两种不等价的Cr与C紧邻共掺体系:CrC_1-TiO_2和CrC_2-TiO_2.CrC_1-TiO_2体系在价带上方出现了主要由C-2p轨道和Cr-3d轨道耦合成的子带.同时,由于姜-泰勒变形效应,Cr-3d轨道的t_(2g)轨道进一步分裂的成Cr-3d_(yz)轨道在导带底形成附加带,有效带隙较纯TiO_2相比变窄了0.84eV.CrC_2-TiO_2体系带隙中有深带隙态存在,由于深间隙态的存在,价带顶到深带隙的能量宽度为0.84eV,电子从价带顶转移到导带底的所需要的能量将大大减小.最后,我们对纯TiO_2和Cr与C紧邻共掺TiO_2的光学特性进行了计算.结果显示Cr与C共掺TiO_2的光学吸收谱都有很好的可见光区域分布,大大提高了太阳光的利用率.     

Ba(Mg1/3Nb2/3)O3电子结构第一性原理计算及光学性能研究

Ba(Mg_1/3Nb_2/3)O₃ (BMN)复合钙钛矿陶瓷具有高介电常数和高品质因子等介电性能, 预示了其在光学领域的应用前景. 本文采用第一性原理方法计算了BMN的电子结构, 对其本征光学性能进行分析和预测. 对固相合成六方相BMN的XRD 测试结果进行Rietveld精修(加权方差因子R_wp=6.73%, 方差因子R_p=5.05%), 在此基础上建立晶体结构模型并对其进行几何优化. 运用基于密度泛函理论(DFT)的平面波赝势方法, 对六方相BMN晶体模型的能带、态密度和光学性质进行理论计算. 结果表明BMN的能带结构为间接带隙, 禁带宽度E_g=2.728 eV. Mg-O和Ba-O以离子键结合为主, Nb-O以共价键结合为主, 费米面附近的能带主要由O-2p和Nb-4d 态电子占据, 形成了d-p轨道杂化. 修正带隙后, 计算了BMN沿[100]和[001]方向上的复介电函数、吸收系数和反射率等光学性质. 结果表明, BMN近乎光学各向同性, 在可见光区, 其本征透过率为77%< T <83%, 折射率为1.91< n <2.14, 并伴随一定的色散现象. 实验测试结果与理论计算结果相吻合.