含铀化合物UAl3和USn3电子结构的密度泛函研究

用第一性原理的全势能LMTO密度泛函能带计算方法研究了具有简单立方Cu3Au结构的含U化合物UX3(X=Al,Sn)的电子结构.对于重原子U的相对论效应,除了用标量相对论加以修正外,还加入了自旋-轨道耦合的修正.研究结果定性地说明了由于不同的交换关联电子势场的作用,在这两种结构相同的含U合金中,U的5f电子态具有完全不同的性质,即在UAl3和USn3中U的5f态分别表现为巡游扩展态和局域态行为,通过Stuttgart-fatband分析,定量地对上述结论予以佐证.同时,还解决了现存的有关理论研究之间的分歧,得出了与实验结果更为相符的上述两种含U合金体系电子结构的计算结果.     

化合物SmCo5的电子结构、自旋和轨道磁矩及其交换作用分析

用自旋极化的MS-Xα方法研究了稀土-过渡族化合物SmCo5₅的电子态密度、自 旋能级劈裂及原子磁矩.研究结果显示，由于化合物中Sm-Co间的轨道杂化效应，使Sm原子原来的5d00空轨道上占据了少量5d电子.由于Co(3d)-Sm(5d)电子间的直接交换作用，导致了Sm-Co间的磁性交换耦合，这是化合物中形成Sm-Co铁磁性长程序的一个重要原因.在SmCo5_{5化合物中存在6个能级呈现负交换耦合，导致了SmCo55化 关键词： 电子结构 自旋极化 原子磁矩 交换耦合}     

多铁材料HoMnO3中光学吸收和畸变驱动的第一性原理研究

六角钙钛矿结构锰氧化物HoMnO₃磁电效应的研究近年来已成为多铁性材料研究中极其重要的一个方面. 本文基于广义梯度近似下的密度泛函理论, 考虑电子自旋的非共线磁性结构, 计算研究了 d电子在位库仑作用和自旋-轨道耦合作用对HoMnO₃的电子结构、 轨道杂化和能态密度分布的影响. 结果显示, 当考虑在位库仑排斥势U作用时, 强烈的Ho 5d与O(3, 4) 2p以及Mn 3d与O(1, 2) 2p间的轨道杂化是驱动HoMnO₃发生铁电畸变的根源, 此时能隙和能带的分布为解释实验中发现的强烈的光学吸收峰提供了理论依据, 而自旋-轨道耦合使得Mn 3d-O(3, 4) 2p在 ab平面内的轨道交迭略有增强, 平面内部分能带简并消除, HoMnO₃材料呈现典型的间接性能隙绝缘体特征. 关键词： 磁电效应 铁电畸变 态密度 光学吸收     

CsNiCl3晶体的光谱精细结构、零场分裂参量及Jahn-Teller效应

应用不可约张量理论构造了三角对称晶场中3d²/3d⁸态离子的45阶可完全对角化的微扰哈密顿矩阵，研究了CsNiCl₃晶体的光谱精细结构、晶体结构、零场分裂参量、Jahn-Telller效应以及自旋单重态对Ni²⁺离子基态能级的影响，理论与实验相符合.在此基础上，进一步研究了以前工作中被忽略的自旋-自旋耦合作用和Trees修正对CsNiCl₃晶体的光谱精细结构和零场分裂参量的影响，发现有四种机理会影响零场分裂参量：1)自旋-轨道耦合机理，2)自旋-自旋耦合机理；3)自旋-轨道与自旋-自旋联合耦合机理；4)自旋-轨道与Trees修正联合耦合机理，其中自旋-轨道耦合机理是最主要的，其他三种机理也是不可忽略的. 关键词： 基态能级 精细结构 零场分裂 自旋-自旋耦合     

掺杂MgCNi3超导电性和磁性的第一性原理研究

从第一性原理出发，计算了MgCNi₃的电子能带结构.MgCNi₃中C 2p与Ni 3d轨道杂化使穿梭费米面上的Ni 3d能带表现出平面性，费米面落在态密度范霍夫奇异(vHs)峰的右坡上.vHs峰上大的电子态密度和铁磁相变点附近的自旋涨落是决定MgCNi₃超导电性的重要因素.研究了三种替代式掺杂对其超导电性和磁性的影响，发现电子掺杂使费米能级下滑到态密度较低的位置，导致体系转变为无超导电性的顺磁相；同构等价电子数的金属间化合物的轨道杂化，引起费米面上态密度的减少，降低了超导电性；而空穴掺杂使费米面向vHs峰值方向移动，虽然费米面上电子态密度增大可能提高超导电性，但增强了的Ni原子磁交换作用产生铁磁序，破坏了超导电性. 关键词： 电子结构 超导电性 磁性 掺杂     

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     

(α,β,γ)-Nb5Si3电子结构和光学性质研究

基于第一性原理的密度泛函理论赝势平面波方法,采用局域密度近似,计算了不同结构的α-Nb₅Si₃,β-Nb₅Si₃和γ-Nb₅Si₃的电子结构、态密度以及光学性质.计算结果表明,Nb₅Si₃费米能级附近价带主要是由Nb的4d轨道及Si的3s和3p轨道贡献,导带主要由Nb的4d轨道贡献;Nb₅Si₃的光学性质具有各向异性的特征,其零频介电常数ε₁（0）=207,折射率n₀=13;在15 eV以上的高能区表现为无色透明.     

稀土金属间化合物CeSn3和CeIn3的能带理论

本文报道了CeSn₃和CeIn₃的能带计算结果。对其f电子的行为,以及f电子与非f原子的s,p,d电子之间的杂化进行了讨论。分析了费密能级附近的态密度分布及能带结构。 关键词：     

正交多铁性材料DyMnO3的磁性质研究

基于密度泛函理论结合投影缀加平面波方法, 通过VASP软件包执行计算, 在分别考虑电子自旋阻挫共线与非共线的磁性结构基础上, 研究了正交结构下多铁性DyMnO₃材料在不同磁性构型下的晶格参数、总能、磁性、电子态密度和能带结构. 计算过程中选取广义梯度近似赝势, 同时使用局域自旋密度近似+U方法处理强关联作用下3d电子的计算结果. 计算结果表明: Mn离子为A型反铁磁态磁性构型的情况下能量最低结构最为稳定, Dy稀土离子磁性甚微, 可忽略不计; 当考虑电子自旋为非共线排列时, 正交DyMnO₃的总能提高、磁矩增大; 从电子结构图分析可知, 材料为间接能隙绝缘体, 能隙宽度约为0.38 eV, 加U后为1.36 eV, 导致晶格畸变的主要原因为Mn-3d与O-2p电子之间强烈的杂化作用. 关键词： 多铁性 反铁磁 密度泛函理论 非共线     

不同组分厚度比的LaMnO3/SrTiO3异质界面电子结构和磁性的第一性原理研究

基于密度泛函理论的第一性原理计算, 研究了(LaMnO₃)_n/(SrTiO₃)_m(LMO/STO)异质界面的离子弛豫、电子结构和磁性质. 研究表明, 不同组分厚度比及界面类型时, 离子弛豫程度各不相同, 并且界面处的电子性质受此影响较大. 对于n型界面, 当LMO的厚度达到6个单胞层后, 电子会从LMO转移到STO, 转移的电子占据界面层Ti原子的3d电子轨道, 界面处出现二维电子气. 对于n型界面(LMO)_n/(STO)₂, 随着LMO厚度数n的增加, 由离子弛豫造成的结构畸变减小, 而界面处Ti原子周围电子的态密度和自旋极化却增大, 表明高厚度比的n型界面有利于产生高迁移率的二维电子气和自旋极化. 而对于p型(LMO)₂/(STO)₈界面, 在STO一侧基本没有结构畸变, 界面处无电子转移和自旋极化现象. 通过计算平均静电势发现n型和p型界面处的势差大小相差2 eV, 解释了p型界面不容易发生电荷转移的原因.     

Electronic structure and magnetism of CeCoGe3

The electronic band structure of CeCoGe₃ has been calculated using the self-consistent full potential nonorthogonal local orbital minimum basis scheme based on density functional theory. We investigated the electronic structure with the spin-orbit interaction and on-site Coulomb potential for the Ce-derived 4f orbitals to obtain the correct ground state of CeCoGe₃. The exchange interaction between local f electrons and conduction electrons play an important role in their heavy fermion characters. The fully relativistic band structure scheme shows that spin-orbit coupling splits the 4f states into two manifolds, the 4f_7/2 and the 4f_5/2 multiplets.     

Ab initio studies on the electronic structure of CeSi5

We investigated the electronic properties of CeSi₅ by band structure calculation based on the density functional theory within LDA, LDA+U, and fully relativistic schemes. The calculated band structure scheme shows that the spin-orbit coupling splits the Ce 4f states into three manifolds. When the on-site Coulomb potential is added to the Ce-derived 4f orbitals, the degeneracy between the f orbitals would be lifted and they are split into lower Hubbard bands and upper Hubbard bands. It was found that quasiparticle mass enhancement inferred by comparing γ to the density of states (DOS) at the Fermi level indicates the effective mass of CeSi₅ is enhanced with the fully relativistic results.     

Th3Ni2B2N3 a possible new superconducting compound: insights from electronic band structure

La₃Ni₂B₂N₃, which is similar to YNi₂B₂C and related borocarbides, was earlier studied by the electronic structure calculations [D.J. Singh, W.E. Pickett, Phys. Rev. B 51 (1995) 8668.], and was predicted to be a 3-D metal. In search of new compounds of the borocarbide and related families to get higher T_C, we have studied the compound Th₃Ni₂B₂N₃, by the first principles full potential electronic structure calculations by the linear augmented plane wave method. We get similar band structure for Th₃Ni₂B₂N₃ as found for La₃Ni₂B₂N₃, and the various atom-split component density of states show similar properties. The total electron density of states at Fermi level has been increased to about 92 states per Ry per f.u. as compared to 57 states per Ry per f.u. in La₃Ni₂B₂N₃. The main increase is due to the increased hybridization of the 5f states as seen by the more prominent low energy tail in the Th-component density of states. Based on this enhancement we predict Th₃Ni₂B₂N₃ to be a high temperature superconductor with a T_c in excess of 30 K.     

Electronic structure and magnetic coupling properties of EuFe2P2: First-principles calculations

We have investigated the electronic structure and magnetic properties of EuFe₂P₂ using first-principles density functional theory within the generalized gradient approximation (GGA)+U schemes. Our calculated ground state magnetic configurations of EuFe₂P₂ is ferromagnetic which Eu²⁺ spins order along c axis. We argue that this kind of magnetic structure of Eu is determined by the indirect RKKY interactions between Eu and direct coupling interaction between Eu 4f with Fe 3d state by our spin-polarized density of states calculations. From the charge density and the Laplace charge density of EuFe₂P₂, we believe that the magnetic moment of Fe is determined by not only Fe-P coupling interactions but also Fe-Fe directly exchange interactions.     

First-principles calculations on TiO2 doped by N, Nd, and vacancy

First-principles density functional theory calculations have been carried out to investigate electronic structures of anatase TiO₂ with substitutional dopants of N, Nd, and vacancy, which replace O, Ti, and O, respectively. The calculation on N-doped TiO₂ with the local density approximation (LDA) demonstrates that N doping introduces some states located at the valence band maximum and thus makes the original band gap of TiO₂ smaller. Examining the effect of the strong correlation of Nd 4f electrons on the electronic structure of Nd-doped TiO₂, we have obtained the half-metallic ground state with the LDA and the insulating ground state with the LDA+U (Hubbard coefficient), respectively. In addition, the calculation on vacancy-doped TiO₂ with the LDA shows that a vacancy can induce some states in the band-gap region, which act as shallow donors.     

Nitrogen doping concentration influence on NaNbO3 from first-principle calculations

The nitrogen concentration effects on electronic band structures and photocatalytic performance of N-doped sodium niobate (NaNbO₃) have been investigated by first-principles calculations based on density functional theory (DFT). At lower nitrogen doping levels, some localized N 2p states are formed above the valence band (O 2p) in N-doped NaNbO₃, leading to the reduction of the photon transition energy in comparison to that of undoped compound. Under higher doping levels, the N 2p states mix with O 2p states and then move the top of valence band upward. Two possible mechanisms for increasing visible light absorbance in N-doped NaNbO₃ are tentatively put forward according to the doping levels, which would be of importance in understanding and developing the visible-light-sensitive nitrogen-doped multimetal oxide.     

LuI3 闪烁晶体的第一性原理研究

采用基于第一性原理的赝势和平面波方法计算了新型闪烁晶体基质材料 LuI₃的结构特性和电子特性. 计算结果表明: -4.4 eV附近有一个宽度约为0.2 eV的窄带, 主要是Lu的4f态; -3.55–0 eV之间的态组成了价带, 这主要是I的5p态; 2.44–12.35 eV之间的态组成了LuI₃的导带, 这主要来源于Lu的5d态, 其中还含有少量的Lu的6s态的贡献. 在-3.46 eV处, Lu的6s态、4f态和I的5p态同时出现了尖峰, 说明相邻的Lu原子的6s态, 4f态与I原子的5p态之间的相互作用强, 出现了杂化峰. 估算出LuI₃晶体的理论光产额约为100000 ph/MeV, 主要得益于LuI₃合适的带隙和能带结构. 关键词： 3')" href="#">LuI₃ 第一性原理 电子结构     

First-principles studies on the electronic structure of ScPd3

The electronic structure and magnetic properties of ScPd₃ have been studied based on the density functional theory within the local-density approximation. In the band structure of ScPd₃, Sc 3d and Pd 4d states play dominant roles near the Fermi level. The fixed spin moment calculation indicates that ScPd₃ has a stable paramagnetic (non-magnetic) state.     

Orbital ordering in Mott-insulators La2O3Fe2Se2 and La2O3Co2Se2

The electronic structure and magnetic properties of new layered oxyselenide compounds La₂O₃Fe₂Se₂ and La₂O₃Co₂Se₂ are studied by first-principles calculations. Our results indicate that both compounds are Mott-insulators with orbital ordering. The ground states of both compounds are the checkerboard antiferromagnetic states, which are different from the iron pnictide superconductors, although their structures are similar to those of the Fe-As-based superconductors.     

Elastic, electronic, and optical properties of hypothetical SnNNi3 and CuNNi3 in comparison with superconducting ZnNNi3

The elastic, electronic, and optical properties of MNNi₃ (M=Zn, Sn, and Cu) have been calculated using the plane-wave ultrasoft pseudopotential technique, which is based on the first-principle density functional theory (DFT) with generalized gradient approximation (GGA). The optimized lattice parameters, independent elastic constants (C₁₁, C₁₂, and C₄₄), bulk modulus B, compressibility K, shear modulus G, and Poisson's ratio υ, as well as the band structures, total and atom projected densities of states and finally the optical properties of MNNi₃ have been evaluated and discussed. The electronic band structures of the two hypothetical compounds show metallic behavior just like the superconducting ZnNNi₃. Using band structures, the origin of features that appear in different optical properties of all the three compounds has been discussed. The large reflectivity of the predicted compounds in the low energy region might be useful in good candidate materials for coating to avoid solar heating.