Te掺杂单层MoS2的电子结构与光电性质

采用基于密度泛函理论的第一性原理计算,研究了Te掺杂对单层MoS₂能带结构、电子态密度和光电性质的影响。结果表明,本征单层MoS₂属于直接带隙半导体材料,其禁带宽度为1.64 eV。本征单层MoS₂的价带顶主要由S-3p态电子和Mo-4d态电子构成,而其导带底则主要由Mo-4d态电子和S-3p态电子共同决定;Te掺杂单层MoS₂为间接带隙半导体材料,其禁带宽度为1.47 eV。同时通过Te掺杂,使单层MoS₂的静态介电常数增大,禁带宽度变窄,吸收光谱产生红移,研究结果为单层MoS₂在光电器件方面的应用提供了理论基础。     

OsSi2电子结构和光学性质的研究

采用基于第一性原理的密度泛函理论赝势平面波方法,对正交相OsSi₂的电子结构、态密度和光学性质进行了理论计算,能带结构计算表明它是一种间接带隙半导体,禁带宽度为0813 eV;其价带主要由Os的5d和Si的3p态电子构成;导带主要由Si的3s,3p以及Os的5d态电子构成;静态介电常数ε₁（0）=1543; 折射率n＝393并利用计算的能带结构和态密度分析了OsSi₂的介电函数、吸收系数、折射率、反射率、 关键词： 2')" href="#">OsSi₂ 第一性原理 电子结构 光学性质     

Ge,Al掺杂锰硅化和物Mn4Si7的第一性原理计算

基于密度泛函理论(DFT)的第一性原理计算方法,对本征Mn₄Si₇以及Ge, Al单掺杂和共掺杂Mn₄Si₇的晶体结构,能带结构,态密度以及光学性质进行了计算和分析.计算结果表明:本征态Mn₄Si₇的禁带宽度为0.810 eV,为直接带隙半导体材料,掺杂后晶体结构稍微变化,禁带宽度减小,且共掺杂时禁带宽度最小,电导率最好.Al以及Ge, Al共同掺杂时会产生杂质能级.掺杂后光子能量向低能级方向移动,光电导率,光吸收,反射系数都有所增大,说明掺杂改善了Mn₄Si₇的光学性质,从而可以提高光伏发电效率.     

萤石结构TiO2的电子结构和光学性质

利用第一性原理计算了立方相萤石TiO₂的晶胞参数,能带结构和电子态密度.结果显示萤石TiO₂属于间接带隙半导体材料,其间接禁带宽度(Γ→X)E_g为2.07eV,比常见的金红石和锐钛矿TiO₂的禁带宽度窄.为了更清楚地了解萤石的光学性质,利用Kramers-Kronig色散关系,分别对萤石和金红石TiO₂的复介电常数、吸收率等参数进行了计算,并将二者结果做了 关键词： 2')" href="#">萤石结构TiO₂ 密度泛函理论 能带结构 光学性质     

LaPO4和ScPO4电子结构和光学性质的第一性原理研究

本文采用基于密度泛函理论的第一性原理平面波赝势方法,对LaPO₄和ScPO₄的能带结构、电子态密度及光学性质进行计算和分析.计算结果表明：LaPO₄的禁带宽度为5.646 eV,ScPO₄的禁带宽度为4.531 eV. LaPO₄晶体价带顶主要由P-3s、P-3p及O-2p态贡献,导带底主要是由La-5d态贡献;ScPO₄晶体价带顶主要由P-3s、P-3p及O-2p态贡献,导带顶主要是由Sc-3d态贡献.就光学性质而言,ScPO₄的静介电常数是2.03,比LaPO₄(1.92)的静介电常数大,体系极化能力较好.     

第一性原理研究In,N共掺杂SnO2材料的光电性质

采用全电势线性缀加平面波(FP-LAPW)的方法,基于密度泛函理论第一性原理结合广义梯度近似(GGA),运用Wien2k软件计算了In, N两种元素共掺杂SnO₂材料的电子态密度和光学性质. 研究表明,共掺杂结构在自旋向下和向上两方向上都出现细的局域能级,两者态密度分布不对称;带隙内自旋向下方向上产生局域能级,共掺化合物表现出半金属性;能带结构显示两种共掺杂化合物仍为直接禁带半导体,价带顶随着N浓度的增加发生向低能方向移动,带隙明显增宽;共掺下的介电函数虚部主介电峰只在8.58 eV 关键词： 电子结构 态密度 能带结构 光学性质     

β-Si3N4电子结构和光学性质的第一性原理研究

采用基于密度泛函的平面波赝势方法(PWP)和广义梯度近似(GGA)，计算了β相氮化硅(β-Si₃N₄)的电子结构和光学性质，得到的晶格常数、能带结构等均与实验结果较好符合.进一步还研究了β-Si₃N₄的光吸收系数以及禁带宽度随外压力的变化规律，为β-Si₃N₄材料在高压条件下的应用提供了理论参考. 关键词： β相氮化硅 电子结构 能带结构 光学性质     

Mg2Sn电子结构及热力学性质的第一性原理计算

采用基于第一性原理的赝势平面波方法系统地计算了Mg₂Sn基态的电子结构、弹性常数和热力学性质.计算结果表明Mg₂Sn的禁带宽度为0.1198eV.运用线性响应方法确定了声子色散关系和态密度,得出Mg₂Sn的热力学性质如等容比热和德拜温度.计算Mg₂Sn的热导率并与实验数据相比较. 关键词： 第一性原理 电子结构 弹性常数 热力学性质     

Co掺杂β-FeSi2电子结构及光学性质的第一性原理研究

采用基于密度泛函理论的第一性原理赝势平面波方法,对不同Co含量的β-FeSi2的能带结构,态密度、分态密度和光学性质进行了计算和比较.几何结构和电子结构的计算结果表明,Co掺杂使得β-FeSi2的晶格常数a增大,b和c变化不大,晶格体积增大.Fe1-xCoxSi2的能带结构变为直接带隙,禁带宽度从0.74 eV减小到0...     

点缺陷对单层MoS2电子结构及光学性质的影响研究

采用基于第一性原理的贋势平面波方法,对不同类型点缺陷单层MoS2电子结构、能带结构、态密度和光学性质进行计算。计算结果表明：单层MoS2属于直接带隙半导体,禁带宽度为1.749ev,V-Mo缺陷的存在使得MoS2转化为间接带隙Eg=0.671eV的p型半导体,V-S缺陷MoS2的带隙变窄为Eg=0.974eV,S-Mo缺陷的存在使得MoS2转化为间接带隙Eg=0.482eV; Mo-S缺陷形成Eg=0.969eV直接带隙半导体,费米能级上移靠近价带。 费米能级附近的电子态密度主要由Mo的4d态和s的3p态电子贡献。光学性质计算表明：空位缺陷对MoS2的光学性质影响最为显著,可以增大MoS2的静态介电常数、折射率n0和反射率,降低吸收系数和能量损失。     

Effect of p-d hybridization and structural distortion on the electronic properties of AgAlM2(M=S,Se,Te) chalcopyrite semiconductors

We report an ab initio calculation and study of the structural and electronic properties of AgAlM₂(M=S,Se,Te) chalcopyrite semiconductors using the density functional theory (DFT)-based self-consistent tight-binding linear muffin tin orbital (TB-LMTO) method. The calculated equilibrium values of the lattice constants, anion displacement parameter (u), tetragonal distortion (η=c/2a) and bond lengths are in good agreement with experimental values. Our study suggests these semiconductors to be direct band gap semiconductors with band gaps 1.98 eV, 1.59 eV and 1.36 eV, respectively. These values are in good agreement with experimental values, within the limitation of the local density approximation (LDA). Our explicit study of the effects of anion displacement and p-d hybridization show that the band gap increases by 9.8%, 8.2% and 5.1%, respectively, for AgAlM₂(M=S,Se,Te) due to former effect and decreases by 51%, 47% and 42%, respectively, due to latter effect.     

Bi2Te3-xSex(x≤3)同晶化合物电子结构的第一性原理研究

本文采用基于密度泛函理论的第一性原理全势能线性缀加平面波方法(FLAPW),分析了Bi₂Te_3-xSe_x体系中各原子自旋轨道耦合(SOI)的p_1/2修正对体系性质的影响,并对Bi₂Te_3-xSe_x(x≤3)同晶化合物的电子特性进行系统的理论研究,首次计算出Bi₂S 关键词： 2Te_3-xSe_x(x≤3)同晶化合物')" href="#">Bi₂Te_3-xSe_x(x≤3)同晶化合物 第一性原理 电子结构 自旋轨道耦合     

Electronic properties of chalcopyrite CuAlX2(X=S,Se,Te) compounds

We present results of the band structure and density of states for the chalcopyrite compounds CuAlX₂ (X=S,Se,Te) using the state-of-the-art full potential linear augmented plane wave (FP-LAPW) method. Our calculations show that these compounds are direct band gap semiconductors. The energy gap decreases when S is replaced by Se and Se replaced by Te in agreement with the experimental data. The values of our calculated energy gaps are closer to the experimental data than the previous calculations. The electronic structure of the upper valence band is dominated by the Cu-d and X-p interactions. The existence of Cu-d states in the upper valence band has significant effect on the optical band gap.     

Theoretical orbital energy spectra of electrons in chemisorbed systems: Chalcogens on Ni(001)

Theoretical energy level spectra calculated by the localised orbital pseudopotential method are presented for chemisorbed O, S, Se and Te monolayers on Ni(001). Adsorption-induced features are a band of bonding states 2–3 eV wide centred ≈ 4 eV below E_f and a band of states centred near E_f. Supporting experimental evidence is discussed.     

Trends in the band-gap pressure coefficients and bulk moduli in different structures of ZnGa2S4, ZnGa2Se4 and ZnGa2Te4

We have performed a first-principles investigation for the family of compounds ZnGa2X4 (X = S, Se, Te). The properties of two possible structures, defect chalcopyrite and defect famatinite are both calculated. We reveal that ZnGa2S4 and ZnGa2Se4 have direct band gaps, while ZnGa2Te4 has an indirect band gap. The local density approximation band gaps are found to be very different in two structures, while the lattice parameters and bulk moduli are similar. We extend Cohen’s empirical formula for zinc-blende compounds to this family of compounds. The pressure coefficients are calculated and metallization pressures are discussed. We find that agi remains fairly constant when the group-Ⅵ element X is varied in ZnGa2X4 (Ⅱ-Ⅲ2 -Ⅵ4 ).     

Valence band photoemission study of the copper chalcogenide compounds, Cu2S, Cu2Se and Cu2Te

The electronic structures of the copper chalcogenide compounds, Cu₂S, Cu₂Se and Cu₂Te have been investigated by taking photoemission data with synchrotron photon sources. The band calculations are done using the full-potential linear-muffin-tin-orbital method. Since the crystal structures are not clarified well, several simplified structure models are used. The calculated densities of states are compared with the observed spectra. The analysis shows that a sharp peak at −3.5 eV is due to the Cu 3d states, and that the tails at the high and low energy sides of the Cu 3d peak are due to the chalcogen p states.     

Ab initio band structure calculations of the low-temperature phases of Ag2Se, Ag2Te and Ag3AuSe2

Ab initio band structure calculations were performed for the low-temperature modifications of the silver chalcogenides β-Ag₂Se, β-Ag₂Te and the ternary compound β-Ag₃AuSe₂ by the local spherical wave (LSW) method. Coordinates of the atoms of β-Ag₂Se and β-Ag₃AuSe₂ were obtained from refinements using X-ray powder data. The structures are characterized by three, four and five coordinations of silver by the chalcogen, a linear coordination of gold by Se, and by metal-metal distances only slightly larger than in the metals. The band structure calculations show that β-Ag₃AuSe₂ is a semiconductor, while β-Ag₂Se and β-Ag₂Te are semimetals with an overlap of about 0.1-0.2 eV. The Ag 4d and Au 5d states are strongly hybridized with the chalcogen p states all over the valence bands. β-Ag₂Se and β-Ag₂Te have a very low DOS in the energy range from about −0.1 to +0.5 eV. The calculated effective mass β-Ag₂Se is about 0.1-0.3 m_e for electrons and 0.75 m_e for holes, respectively.     

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 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.     

Positron annihilation characteristics of positronium oxides,sulfides, etc. [X=e+]: Implications for oxide and sulfide crystals

Theoretical Hartree-Fock calculation are summarized for the [X⁼e⁺] systems with X = O, S, Se, and Te which establish the stability of bound states for the system. The two-photon annihilation lifetime, τ, and angular correlation, N(θ), are calculated and positron annihilation from alkaline earth oxides is discussed.