Structural,electronic,optical,and magnetic properties of Co-doped Cu_2O

We investigate the magnetic properties of Co-doped Cu_2O. We studied first the electronic and structural properties of Cu_2O using the optimization of the lattice constant which is 4.18 . The calculated gap is found between 0.825 eV and1.5 eV, these values are in good agreement with the experimental results. The Co atoms are inserted in Cu_2O by means of the density functional theory(DFT) using LSDA, LSDA +U, and LSDA + MBJ approximations in the WIEN2 k code, based on the supercell model by setting up 12, 24, and 48 atoms in(1×1 × 2),(1 × 2 × 2), and(2 × 2×2) supercells respectively with one or two copper atoms being replaced by cobalt atoms. The energy difference between the ferromagnetic and antiferromagnetic coupling of the spins located on the substitute Co has been calculated in order to obtain better insight into the magnetic exchange coupling for this particular compound. The studied compound exhibits stable integer magnetic moments of 2 μBand 4 μBwhen it is doped with 2 atoms of Co. Optical properties have also been worked out. The results obtained in this study demonstrate the importance of the magnetic effect in Cu_2O.     

Electronic structure and magnetic properties of substitutional transition-metal atoms in GaN nanotubes

The electronic structure and magnetic properties of the transition-metal(TM) atoms(Sc–Zn, Pt and Au) doped zigzag GaN single-walled nanotubes(NTs) are investigated using first-principles spin-polarized density functional calculations. Our results show that the bindings of all TM atoms are stable with the binding energy in the range of 6–16 eV. The Sc- and V-doped GaN NTs exhibit a nonmagnetic behavior. The GaN NTs doped with Ti, Mn, Ni, Cu and Pt are antiferromagnetic. On the contrary, the Cr-, Fe-, Co-, Zn- and Au-doped GaN NTs show the ferromagnetic characteristics. The Mn- and Codoped GaN NTs induce the largest local moment of 4μB among these TM atoms. The local magnetic moment is dominated by the contribution from the substitutional TM atom and the N atoms bonded with it.     

First-principles investigation of armchair stanene nanoribbons

In this study, we systematically investigated the structural, electronic and optical properties of armchair stanene nanoribbons (ASNRs) by using the first-principles calculations. First, we performed full geometry optimization calculations on various finite width ASNRs where all the edge Sn atoms are saturated by hydrogen atoms. The buckled honeycomb structure of two dimensional (2D) stanene is preserved, however the bond length between the edge Sn atoms is shortened to 2.77 Å compared to the remaining bonds with 2.82 Å length. The electronic properties of these nanoribbons strongly depend on their ribbon width. In general, band gap opens and increases with decreasing nanoribbon width indicating the quantum confinement effect. Consequently, the band gap values vary from a few meV exhibiting low-gap semiconductor (quasi-metallic) behavior to ～0.4–0.5 eV showing moderate semiconductor character. Furthermore, the band gap values are categorized into three groups according to modulo 3 of integer ribbon width N which is the number of Sn atoms along the width. In order to investigate the optical properties, we calculated the complex dielectric function and absorption spectra of ASNRs, they are similar to the one of 2D stanene. For light polarized along ASNRs, in general, largest peaks appear around 0.5 eV and 4.0 eV in the imaginary part of dielectric functions, and there are several smaller peaks between them. These major peaks redshifts, slightly to the lower energies of incident light with increasing nanoribbon width. On the other hand, for light polarized perpendicular to the ribbon, there is a small peak around 1.6 eV, then, there is a band formed from several peaks from 5 eV to ～7.5 eV, and the second one from 8 eV to ～9.5 eV. Moreover, the peak positions hardly move with varying nanoribbon width, which indicates that quantum confinement effect is not playing an essential role on the optical properties of armchair stanene nanoribbons. In addition, our calculations of the optical properties indicate the anisotropy with respect to the type of light polarization. This anisotropy is due to the quasi-2D nature of the nanoribbons.     

Fe掺杂GaN光电特性的第一性原理研究

基于密度泛函理论体系,计算了本征GaN材料和12.5%的Fe掺杂GaN体系的光电特性,分析了晶体结构、能带结构和电子态分布、介电函数、吸收系数、折射率、反射率、能量损失谱和消光系数,从理论上讨论了掺杂对体系光电特性的影响.计算所得理想GaN的禁带宽度为3.41 eV,Fe的重掺杂体系明显变窄,为3.06 eV,但仍为直接带隙半导体.本征GaN材料与Fe掺杂GaN体系的静态介电常数为5.74和6.20,折射率为2.39和2.48,能量损失最大值在20.02 eV和18.96 eV,最大吸收系数能量均在13.80 eV左右.计算结果为Fe掺杂GaN高压光电导开关材料及器件的进一步研究提供了有力的理论依据和实验支持.     

Electronic and optical properties of black phosphorus doped with Au,Sn and I atoms

In this study, the electronic and the optical properties of monolayer black phosphorus (BP) doped with Gold (Au), Tin (Sn) and Iodine (I) atoms have been investigated by the density-functional theory (DFT) method. In the calculations, the electronic and the optical properties of monolayer BP have been substantially changed with doping. Monolayer BP has a narrow bandgap as 0.85 eV, BP doped with these atoms, results in a metallic behaviour and nearly spin gapless band gap behaviour. The dielectric constant of BP which shows anisotropic optical properties due to different edge states as zigzag and armchair has been changed with doping especially with Au.     

应变对两层半氢化氮化镓薄膜电磁学性质的调控机理研究

采用基于密度泛函理论的第一性原理模拟计算,研究了在应变作用下两层半氢化氮化镓纳米薄膜的电学和磁学性质.没有表面修饰的两层氮化镓纳米薄膜的原子结构为类石墨结构,并具有间接能隙.然而,当两层氮化镓纳米薄膜的一侧表面镓原子被氢化时,该纳米薄膜却依然保持纤锌矿结构,并且展示出铁磁性半导体特性.在应变作用下,两层半氢化氮化镓纳米薄膜的能隙可进行有效调控,并且它将会由半导体性质可转变为半金属性质或金属性质.这主要是由于应变对表面氮原子的键间交互影响和p-p轨道直接交互影响之间协调作用的结果.该研究成果为实现低维半导体纳米材料的多样化提供了有效的调控手段,为其应用于新型电子纳米器件和自旋电子器件提供重要的理论指导.     

二氧化铀电子结构和弹性性质的第一性原理研究

本文采用第一性原理的方法系统研究了UO₂的晶体结构、电子结构和弹性性质. 在计算中采用广义梯度近似结合Hubbard U项描述电子的局域强关联效应. 首先通过计算能带带隙大小并与理论值比较的方法, 得到了合理的有效库仑相关作用能(U_eff)的取值, 同时通过态密度的计算, 进一步验证了U_eff取值的合理性. 计算得到UO₂中U原子的U_eff值为3.30 eV (U_eff=U-J, U=3.70 eV, J=0.40 eV). 应用此参数计算得到的UO₂晶格常数为5.54 Å, 带隙宽度为2.17 eV. 该结果优于目前现有的研究结果, 同时在同样的U_eff值条件下计算所得到的弹性常数与实验值也符合得较好. 相较于之前的基于实验测量并分析得到的U_eff值, 我们所采用的方法在对UO₂性质描述上更为准确. 不同的有效库仑相关作用能取值下的态密度结果表明, 有效库仑相关作用能的大小可以影响铀原子5f电子轨道的分布.     

Tuning the magnetic and electronic properties of strontium titanate by carbon doping

The magnetic and electronic properties of strontium titanate with different carbon dopant configurations are explored using first-principles calculations with a generalized gradient approximation (GGA) and the GGA+U approach. Our results show that the structural stability, electronic properties and magnetic properties of C-doped SrTiO₃ strongly depend on the distance between carbon dopants. In both GGA and GGA+U calculations, the doping structure is mostly stable with a nonmagnetic feature when the carbon dopants are nearest neighbors, which can be ascribed to the formation of a C–C dimer pair accompanied by stronger C–C and weaker C–Ti hybridizations as the C–C distance becomes smaller. As the C–C distance increases, C-doped SrTiO₃ changes from an n-type nonmagnetic metal to ferromagnetic/antiferromagnetic half-metal and to an antiferromagnetic/ferromagnetic semiconductor in GGA calculations, while it changes from a nonmagnetic semiconductor to ferromagnetic half-metal and to an antiferromagnetic semiconductor using the GGA+U method. Our work demonstrates the possibility of tailoring the magnetic and electronic properties of C-doped SrTiO₃, which might provide some guidance to extend the applications of strontium titanate as a magnetic or optoelectronic material.     

强关联效应下非磁性元素Ir掺杂的SmFeAsO电子结构理论研究

基于密度泛函理论, 采用广义梯度近似方法 (SGGA+U) 计算分析了SmOFeAs电子结构以及 Ir 掺杂对该体系晶体结构和电子结构的影响. 结果表明, 随着Ir的掺杂, SmOFeAs晶体结构中FeAs层与SmO层之间的耦合增强, 晶体内部所含的铁砷四面体随着Ir掺杂其畸变性程度逐步减小. Fe3d以及As4p杂化轨道对体系电子结构起主要影响作用. Ir掺杂所引入的电子使FeAs层的巡游电子增多、Fe3d轨道中的 d_z2轨道离域性增强. 当Ir掺杂量为20%时, 费米面处于电子态密度峰值附近, 费米面急剧变化使该体系的T_c值有所增高, 反映了体系费米能级移动与其超导电性的密切关联性. 计算的电子态密度与XPS所得价带谱实验结果一致, 进一步验证了采用SGGA+U方法其包含修正d轨道局域电子的库仑势, 使得计算结果与实验结果更加接近. 关键词： U')" href="#">GGA+U SmOFeAs 晶体结构 电子结构     

金属元素掺杂对TiAl合金力学性能的影响

利用基于密度泛函理论的第一性原理方法研究了金属元素X (X分别表示V, Nb, Ta, Cr, Mo和W)掺杂对TiAl合金性能的影响. 研究发现, 掺杂可以有效减小合金的各向异性, 增强Ti-Al 原子间的相互作用, 同时增强金属键性, 减弱共价键性, 有利于塑性变形. 在相同的压力下, 不同的掺杂浓度和掺杂元素对体积的影响不同. 通过计算不同掺杂体系的弹性常数、体弹模量和剪切模量可知: 当掺杂浓度为6.25%时, 相对于V, Nb和Ta, Cr, Mo和W掺杂能较好地改善TiAl金属间化合物的韧性; 当掺杂浓度为12.5%时, 相对其他掺杂元素Mo的韧化作用最强. 从Mo掺杂后TiAl体系的分波态密度和电荷密度图, 发现Mo和Ti 原子发生强烈的s-s, p-p, d-d电子相互作用, 有效地束缚了合金中Ti和Al原子的迁移, 有助于提高合金的稳定性和强度.     

Effects of alloying element on stabilities,electronic structures,and mechanical properties of Pd-based superalloys

The thermodynamic stabilities, electronic structures, and mechanical properties of the Pd-based superalloys are studied by first principles calculations. In this work, we discuss the effect of Pd-based superalloys made from Al, Si, Sc, Ti,V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, Mo, Tc, Hf, Ta, W, Re, Os, Ir and Pt, and we also calculate a face centered cubic(fcc)structure 2 × 2 × 2 superalloy including 31 Pd atoms and one alloying element T M(Pd_(31)TM). The mixing energies of these Pd-Based superalloys are negative, indicating that all Pd-based superalloys are thermodynamically stable. The Pd_(31)Mn has the lowest mixing energy with a value of-0.97 eV/atom. The electronic structures of the Pd-based superalloys are also studied, the densities of states, elastic constants and moduli of the mechanical properties of the Pd-based superalloys are determined by the stress-strain method and Voigt–Reuss–Hill approximation. It is found that Pd_(31)TM is mechanically stable, and Pd_(31)Tc has the largest C_(11), with a value 279.7 GPa. The Pd_(31)Cr has the highest bulk modulus with a value of299.8 GPa. The Pd_(31)Fe has the largest shear modulus and Young's modulus with the values of 73.8 GPa and 195.2 GPa,respectively. By using the anisotropic index, the anisotropic mechanical properties of the Pd_(31)T M are discussed, and threedimensional(3 D) surface contours and the planar projections on(001) and(110) planes are also investigated by the Young modulus.     

缺陷黄铜矿结构Xga2S4 (X=Zn,Cd, Hg)晶体电子结构和光学性质的第一性原理研究

采用基于密度泛函理论(DFT)的第一性原理超软赝势方法对缺陷黄铜矿结构XGa₂S₄ (X=Zn, Cd, Hg)晶体的晶格结构、电学以及光学性质进行了对比研究. 分析比较了它们的晶格常数、键长、能带结构、态密度、介电函数、折射率和反射系数等性质, 并总结其变化趋势. 结果表明: 这三种材料的光学性质在中间能量区域(4 eV–10 eV)表现出较强的各向异性, 而在低能区域(<4 eV)和高能区域(>10 eV)各向异性较弱. ZnGa₂S₄和HgGa₂S₄两种材料的折射率曲线在等离子体频率ω_p处有一明显的拐点, 反射系数在ω_p处达到最大值后急剧下降. 三种晶体的强反射峰均处于紫外区域, 因此可以用作紫外光屏蔽或紫外探测材料. 关键词： 缺陷黄铜矿结构 电子结构 光学性质 第一性原理计算     

Electronic structure and optical properties of Mg_xZn_(1-x)S bulk crystal using first-principles calculations

We perform the first-principles calculations within the framework of density functional theory to determine the elec- tronic structure and optical properties of MgxZnl-xS bulk crystal. The results indicate that the electronic structure and optical properties of MgxZnl_xS bulk crystal are sensitive to the Mg impurity composition. In particular, the MgxZnl-xS bulk crystal displays a direct band structure and the band gap increases from 2.05 eV to 2.91 eV with Mg dopant compo- sition value x increasing from 0 to 0.024. The S 3p electrons dominate the top of valence band, while the Zn 4s electrons and Zn 3p electrons occupy the bottom of conduction band in MgxZnl_xS bulk crystal. Moreover, the dielectric constant decreases and the optical absorption peak obviously has a blue shift. The calculated results provide important theoretical guidance for the applications of MgxZn1-xS bulk crystal in optical detectors.     

不同浓度Ag掺杂ZnO电子结构和光学性质的第一性原理研究

基于密度泛函理论框架下的第一性原理计算方法,研究了不同浓度Ag掺杂ZnO体系的电子结构和光学性质。计算结果表明,不同浓度Ag原子代替Zn原子后会导致电子结构和光学性质有显著的改变,能带随掺杂浓度的增大带隙渐渐变窄,光吸收、反射等也随银掺杂浓度的增大先是向高能端偏移再向低能端移动。这暗示Ag掺杂ZnO对其电子结构及光学性质有很大的影响,为进一步研究掺杂对ZnO性质的影响提供理论基础。     

稀土元素Lu，Sc掺杂GaN光电特性的第一性原理研究

基于密度泛函理论,采用广义梯度近似（GGA+U）平面波超软赝势方法,计算了本征GaN和稀土元素Lu、Sc掺杂GaN体系的电子结构和光学性质.结果表明：计算得到本征GaN的禁带宽度为3.37 eV,与实验值（3.39 eV）接近. Lu掺杂后GaN体系带隙变窄,而Sc掺杂后诱导了深能级杂质,带隙变宽,但仍为直接带隙半导体.掺杂后体系均发生畸变,晶格常数和体积增大,且在费米能级附近产生杂质带. Lu、Sc掺杂GaN体系的静态介电常数较本征GaN（4.50）均有所增大.Lu、Sc掺杂后体系介电常数虚部整体左移,光吸收边往低能方向移动,发生了红移现象.计算结果对稀土元素Lu、Sc掺杂GaN高压光电材料的开发和研究提供了理论依据.     

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.     

Nb掺杂γ-TiAl金属间化合物的电子结构与力学性能

运用基于密度泛函理论的第一性原理方法计算了Nb掺杂γ-TiAl金属间化合物的结构参数、能带结构、电子态密度及弹性常数.结果表明:Nb替代Ti掺杂相比Nb替代Al掺杂的形成能低,Nb在替位掺杂时更倾向于取代Ti原子形成稳定的结构,Nb替代Ti掺杂能够提高γ-TiAl金属间化合物的抵御塑性变形能力、断裂强度和延展性;与Nb替代Ti掺杂相比,Nb替代Al掺杂同样增强γ-TiAl金属间化合物的断裂强度且其增强延展性的效果更好,但抵御塑性变形的能力有所削弱.     

Electron screening effect in the reactions He(d, p)He and d(He, p)He

The cross section of the reactions ³He(d, p)⁴He and d(³He, p)⁴He has been measured at the center-of-mass energies E=5 to 60 keV and 10 to 40 keV, respectively. The experiments were performed to determine the magnitude of the electron screening effect leading to the respective electron-screening potential energy U_e=219±7 and 109±9 eV, which are both significantly higher than the respective values from atomic physics models, U_e=120 and 65 eV.     

First principle study of cubic perovskites: AgTF3 (T=Mg, Zn)

The structural, electronic and optical properties of AgTF₃ (T=Mg, Zn) are calculated for the first time using the full-potential linearized augmented plane wave method within the generalized gradient approximation. Structural parameters of the compounds are found to be in reasonable agreement with the available literature. Both compounds are found to have narrow and indirect band-gaps. The calculated band gap for AgMgF₃ is 0.78 eV and 0.75 eV for AgZnF₃. It is observed that Ag-4d, Zn-3d and Ag-5s states controls the electronic properties of AgMgF₃ and AgZnF₃. The nature of chemical bonding in these compounds is discussed by the electron density plots. The results of complex dielectric constant, refractive index, normal-incidence reflectivity and optical conductivity are also presented in the incident photon energy range of 0-35 eV. The wide absorption energy range makes these materials suitable for different devices applications.     

Study of the optical-electrical characteristics of InxGa1−xN alloy with low in doping

The electronic structures and optical properties of In doped GaN were calculated with different doping concentration, from first-principles using density function theory with the plane-wave ultrasoft pseudopotential method. The influence of In doping on the volume, interactions among atoms, density of states, electron density difference, and optical properties of GaN was analyzed. The results show that the interactions among atoms are reduced, band gap decreases, and absorption spectra have red shift along with the increase of In doping concentration.