CrSi2能带结构和光学性质的第一性原理研究

采用基于第一性原理的密度泛函理论（DFT）赝势平面波方法，对CrSi2的能带结构、态密度和光学性质进行了理论计算，能带结构计算表明CrSi2属于一种间接带隙半导体，禁带宽度为0．353eV,其能态密度主要由Cr的3d层电子和Si的3p层电子的能态密度决定；计算了CrSi2的介电函数、反射率、折射率及吸收系数等。经比较，计算结果与已有的实验数据符合较好。     

Mg2Si电子结构及光学性质的研究

采用基于第一性原理的赝势平面波方法系统地计算了Mg2Si基态的电子结构、态密度和光学性质。计算结果表明Mg2Si属于间接带隙半导体，禁带宽度为0．2994eV；其价带主要由Si的3p以及Mg的3s、3p态电子构成，导带主要由Mg的3s、3p以及Si的3p态电子构成；静态介电常数ε1（0）=18．89；折射率n0=4．3460；吸收系数最大峰值为356474．5cm^-1；并利用计算的能带结构和态密度分析了Mg2Si的介电函数、折射率、反射率、吸收系数、光电导率和能量损失函数的计算结果，为Mg2Si的设计与应用提供了理论依据。     

K掺杂立方相Ca2Si电子结构及光学性能的研究

基于第一性原理的密度泛函理论赝势平面波方法,采用广义梯度近似（GGA）对掺K的立方相Ca2Si的电子结构和光学性能,包括能带结构、态密度、介电函数、折射率、反射率、吸收系数、光电导率及能量损失函数进行理论计算,结果表明,掺K后立方相Ca2Si的能带向高能方向发生了偏移,形成直接带隙的P型半导体,禁带宽度为0.6230eV,光学带隙变宽,价带主要是Si的3p、Ca的4s、3d以及K的3p、4s态的贡献;静态介电函数ε1（0）=14.4;折射率n0=3.8;吸收系数最大峰值为3.47×105cm-1。通过掺杂调制材料电子结构和光电性能,为Ca2Si材料光电性能的开发与应用提供了理论依据。     

新型稀磁半导体母体YCuSO第一性原理计算

利用基于密度泛函理论的第一性原理赝势平面波方法,计算了新型稀磁半导体母体YCuSO的能带结构和态密度以及介电函数、反射函数和吸收函数等光学性质.计算结果表明,YCuSO属于直接带隙半导体,禁带宽度约为1.22 eV.其费米面主要由Cu 3d和S 3p层电子构成.YCuSO半导体晶体在80~90 nm处存在明显的光损失,在80~350 nm区间光反射较大,光吸收主要发生在50~680 nm区间,表明YCuSO在红外与远紫外波段具有潜在的应用价值.这些结果为实验室合成基于YCuSO母体、电荷自旋注入机制分离的新型稀磁半导体,进而研究其性质提供了依据.     

Sn掺杂Ga_(1.375)In_(0.625)O_3透明导电氧化物的第一性原理计算

用第一性原理计算了Sn替位Ga1.375In0.625O3化合物的Ga原子(Ga1.25In0.625Sn0.125O3)和Sn替位Ga1.375In0.625O3化合物的In原子(Ga1.375In0.5Sn0.125O3)的结构、电子能带和态密度。Ga1.25In0.625Sn0.125O3半导体材料比Ga1.375In0.5Sn0.125O3材料具有大的晶胞体积和强的Sn-O离子键。在Sn掺杂Ga1.375In0.625O3半导体中,Sn原子优先取代In原子。Sn掺杂Ga1.375In0.625O3半导体显示n型导电性,杂质能带主要由Sn 5s态组成。Ga1.375In0.5Sn0.125 O3半导体的光学带隙大于Ga1.25In0.625Sn0.125O3半导体的光学带隙。Ga1.25In0.625 Sn0.125 O3具有小的电子有效质量,Ga1.375In0.5Sn0.125O3具有多的相对电子数。     

β-CaSiO3晶体的电子结构及光学性质

基于第一性原理的平面波赝势方法(PWP)的局域密度近似(LDA)/广义梯度近似(GGA)计算了β-Ca-SiO3的几何结构、能带结构、态密度和光学性质。其晶胞参数优化结果与实验相比,LDA/GGA的相对误差为-3.62%/1.91%。对优化后的β-CaSiO3晶体进行能带结构分析表明,β-CaSiO3晶体为间接带隙结构,禁带宽度Eg(LDA)=5.53eV,Eg(GGA)=5.18eV。对态密度图及Mulliken电荷分布的分析表明,Ca的d轨道有电子分布,即Ca的s、p、d轨道均参与了成键。β-CaSiO3晶体中Ca与SiO3基团之间形成的化学键主要是离子键,而Si与O之间的化学键是共价键。     

第一性原理研究InP的能带结构与光学性能

采用基于局域密度近似的第一性原理方法计算了InP的能带结构和电子态密度,并对InP晶体的电荷分布进行了Mulliken布局分析.计算表明InP是直接带隙半导体材料,其价带主要由In的5s以及P的3s、3p态电子构成,导带主要由P的3p以及In的5s、5p态电子构成;P原子与In原子的电子重叠布局数达2.30,表明In-P键的共价性较强而离子性较弱.利用Kramers-Kronig色散关系对InP的介电函数、能量损失谱、折射率以及吸收系数等进行了计算,计算结果与实验值基本一致.此外,根据计算的能带结构与态密度分析了InP电子结构与光学性质的内在联系,解释了InP材料光学性能的微观机制.     

（001）应变对正交相Ca2P0.25Si0.75能带结构及光学性质的影响

为了研究(001)应变对正交相Ca2P0.25Si0.75能带结构及光学性质的影响,采用第一性原理贋势平面波方法对(001)应变下正交相Ca2P0.25Si0.75的能带结构及光学性质进行了模拟计算.计算结果表明:晶格(001)面发生100%~116%张应变时,带隙随着应变增加而减小;在晶格发生88%~100%压应变时,带隙随着张应变的增加而增加;84%~88%压应变时,带隙随着压应变的增加而减小.当施加应变后光学性质发生显著的变化:随着压应变的增加,静态介电常数、折射率逐渐减小,张应变则增大.施加压应变反射向高能方向偏移,施加张应变反射向低能方向偏移,但施加应变对反射区域的影响不显著.施压应变吸收谱、光电导率的变化与介电函数和折射率相反.综上所述,(001)应变改变了Ca2P0.25Si0.75的电子结构和光学常数,是调节Ca2P0.25Si0.75光电传输性能的有效手段.     

单点缺陷氧化石墨烯电子结构与光学特性的第一性原理研究

本研究采用基于密度泛函理论的第一性原理方法, 在局域密度近似和广义梯度近似下, 研究了单点缺陷下不同结构氧化石墨烯的电子结构和光学特性。研究结果表明: 文中四种构型的氧化石墨烯为力学稳定结构, 其中包含不饱和氧原子的氧化石墨烯结构在水裂解及制氢中具有重要应用潜力。能带及分波态密度计算结果表明, 包含不饱和氧原子的构型为间接带隙半导体, 其余构型均为直接带隙半导体, 且掺杂类型和带隙值随结构不同而改变。氧化石墨烯的光学吸收表现为各向异性, 且在垂直于平面方向上的吸收边蓝移到近紫外可见光区。包含sp ³杂化形式的结构光学吸收系数比包含sp ²杂化的结构高, 说明碳氧双键和悬挂键的存在对吸收光谱有重要影响。     

Al和S共掺杂金红石型TiO2第一性原理研究

利用密度泛函理论体系下的第一性原理平面波超软赝势法,研究Al单掺杂和S单掺杂以及Al/S共掺杂金红石相TiO_2的能带结构、态密度和光学性质。结果表明:Al单掺杂导致禁带宽度减小为1.79eV,并且在价带上方形成了一条杂质能带;S单掺杂导致费米能级上移靠近导带,直接带隙减小为0.816eV;Al/S共掺杂导致能带结构中出现了3条杂质能带,直接带隙约0.841eV,杂质能级主要由Al原子的3p轨道和S原子的3p轨道组成。Al/S共掺杂后使TiO_2的吸收带产生红移,在可见光区具有较大的吸收系数,能够增强电子传输能力和抑制电子空穴对复合。     

Optical and transport properties and electronic structure of nickel doped arsenic chalcogenides

The electronic structure of monoclinic As₂X₃ (X = S, Se) is investigated using full potential linearized augmented plane wave method in the framework of density functional theory. From energy bands and the density of states it is seen that the lone pair p-states of sulfur/selenium contribute closest to Fermi energy level. Introduction of transition metal impurities such as Nickel modifies the semiconducting gap in As₂S₃ and As₂Se₃. The crystal field splits the Ni 3d bands with t_2g electrons in the valence band and e_g electrons in conduction band. We compute optical properties like the complex dielectric functions, refractive indices, absorption coefficient, reflectance, etc. The low symmetry chalcogenides exhibit optical dichroism. On doping, As₂S₃ and As₂Se₃ show additional losses in the IR regions, which indicates allowed interband transitions due to available 3d-states in the valence and conduction bands. A narrow transparent window in the visible region is available in Ni_0.5As_1.5Se₃ crystals. Important transport properties such as Seebeck and Hall coefficients, and carrier concentration are computed. It is seen that these high resistivity chalcogenides are n-type semiconductors.     

Theoretical investigation of atomic structure and electronic properties of Ca/Si(110)-(2 × 1) reconstruction

We have presented first-principles total-energy calculations for the adsorption of Ca metals onto a Si(110) surface. The density functional method was employed within its local density approximation to study the atomic and electronic properties of the Ca/Si(110) structure. We considered the (1 × 1) and (2 × 1) structural models for Ca coverages of 0.5 monolayer (ML) and 0.25 ML, respectively. Our total-energy calculations indicate that the (1 × 1) phase is not expected to occur. It was found that Ca adatoms are adsorbed on top of the surface and form a bridge with the uppermost Si atoms. The Ca/Si(110)-(2 × 1) produces a semiconducting surface band structure with a direct band gap that is slightly smaller than that of the clean surface. One filled and two empty surface states were observed in the gap; these empty surface states originate from the uppermost Si dangling bond states and the Ca 4 s states. It is found that the Ca-Si bonds have an ionic nature and complete charge being transferred from Ca to the surface Si atoms. Finally, the key structural parameters of the equilibrium geometry are detailed and compared with the available results for metal-adsorbed Si(110) surface, Ca/Si(001), and Ca/Si(111) structures.     

The doping effect of N substituting for different atoms in orthorhombic SrHfO<Subscript>3</Subscript>

The first-principles density-functional theory has been carried out to study the structural, electronic, and optical properties of N-doped orthorhombic SrHfO₃. The calculated results show the doping of N substituting for O is most favorable. When the doping of N substituting for Hf(Sr), the impurity energy level of N 2p states is introduced in the forbidden band. When the doping of N substituting for O1(O2), the width of the valence bands increases due to the presence of N 2p states in the top of valence bands. The doping of N resulting in red-shift has been studied by analysing the imaginary part of dielectric function e₂ (w) \varepsilon_{2} (\omega ) of N-doped orthorhombic SrHfO₃.     

四面体掺杂尖晶石结构Co1-xRexCr2O4(Re=Li、Na、K、Rb)的电子结构和光学性质

采用基于密度泛函理论(DFT)的平面波超软赝势方法, 计算了CoCr₂O₄及Li、Na、K和Rb四面体掺杂CoCr₂O₄的基态结构、电子结构和光学性质。计算结果表明: 一价离子四面体掺杂都导致晶格有微小的畸变, 使体系的稳定性降低, Rb掺杂的体系最稳定; 电子态密度的计算结果表明: 掺杂体系的导带主要有Co-3d和Cr-3d轨道电子构成, 掺杂离子改变了CoCr₂O₄导带的电子结构, 主要引起了导带Co-3d态密度峰的下移, 随着掺杂浓度的增大, 费米能级进入价带更深; 光学性质计算表明: 掺杂体系的吸收光谱发生红移, 并在低能区有很强的吸收, 表明掺杂能极大地提高CoCr₂O₄对可见光的吸收和光催化效率。     

First-principles Calculations of Structural,Magnetic Electronic and Optical Properties of Rare-earth Metals TbX (X=N,O, S,Se)

The structural, magnetic, electronic and optical properties of Terbium-based binaries (TbX) (X = N, O, S and Se) in two cubic structures NaCl and CsCl have been investigated. This study is carried out by Full-Potential linearized Muffin-Tin orbitals (FP-LMTO) method in the framework of the functional theory of density (DFT) implemented in the lmtart code. The presence of f-state electrons in these induced high-correlation materials led us to study these systems using local density approximation (LDA) for the paramagnetic state and spin local density approximation (LSDA) for the ferromagnetic state within two cubic structures. We have demonstrated that these binaries are stable in the ferromagnetic state in the cubic phase of NaCl, which allows us to deduce the magnetic moments of these components. From the electronic band structures and density states, we have concluded that TbX (X = N, O, S and Se) are metallic in the NaCl phase. The results obtained in this work show that the theoretical parameters of the ground state, structure of the bands, density of the states (DOS) and optical properties agree well with other available theoretical and experimental data.     

Electronic band structure of metallic lithium in the field of external excitation

A procedure is developed that allows for exact calculations of the band energy of a solid in the Hartree–Fock approximation. The starting point is a self-consistent calculation that employs a Gaussian basis of functions. The method is used to establish the energy structure of the electrons in metallic lithium as a function of temperature. The calculated density of states, optical conductivity, the K-edge of the X-ray emission spectrum, and other properties of the electrons agree with the experimental data. Small variations in the band energies for lithium are discovered. The most important ones are the broadening of the core electron states and the transition of outer-shell electrons from s-symmetry stats to p-symmetry states as the temperature grows. Influence of vacancies and s-, p-, d-impurities on the electronic band structure is investigated. The influence of d-impurities is the most significant.     

First-principles study of electronic and optical properties of Pbnm orthorhombic SrHfO3

The first-principles calculations were carried out to investigate the electronic and optical properties of Pbnm orthorhombic SrHfO₃. The equilibrium lattice constants of Pbnm orthorhombic SrHfO₃ optimized by the localized density approximation (LDA) are in good agreement with experimental values. Electronic structures of Pbnm orthorhombic SrHfO₃ have been studied throughout the calculations of band structure, densities of states (DOS) and charge densities. The band structure shows that Pbnm orthorhombic SrHfO₃ has direct band gap. The DOS and charge densities of Pbnm orthorhombic SrHfO₃ indicate that bonding between Hf and O is mainly covalent whereas bonding between Sr and O is mainly ionic. The complex dielectric function, refractive index, absorption coefficient, energy-loss spectrum, complex conductivity function and reflectivity of Pbnm orthorhombic SrHfO₃ have been predicted. The imaginary and real parts of the calculated complex dielectric function are consistent with the experimental measurements for the amorphous SrHfO₃.