茂金属配合物[(eat5-C5H4R)Mo(CO)3 ]2(R: SiMe3 ,Si2Me5)的电子结构研究

运用G98W ,采用Lanl2dz基组 ,对茂金属配合物 [(eat5 C5H4R)Mo(CO) 3 ]2 (R :SiMe3 ,Si2 Me5)进行从头算研究 ,探讨配合物结构单元的稳定性、分子轨道能量、原子净电荷布居规律 ,以及一些前沿分子轨道的组成特征等 ,结果表明 ,标题配合物结构在能量上是稳定的 ,作为结构单元而存在 .     

三角对称下3d3离子2E态g因子性质研究

采用完全对角化方法,以尖晶石结构的ZnAl2O4:Cr3+,ZnGa2O4:Cr3+和MgAl2O4:Cr3+系列晶体为例,联系晶格局域结构,对三角对称下3d3离子2E态g因子性质进行了研究.研究中考虑了包括自旋与自旋相互作用、自旋与另一轨道相互作用以及轨道与轨道相互作用在内的微小磁相互作用.对ZnAl2O4:Cr3+ 体系2E态g因子给出了理论解释,说明了ZnGa2O4:Cr3+体系的g‖(E′)应为负值,并从理论上预测了MgAl2O4:Cr3+体系2E态g因子数值.研究表明,微小磁相互作用对2E态g因子的贡献较大,在计算中是不可忽略的;相对于基态g因子来说,2E态g因子随晶格局域结构变化较为敏感.     

钒氧酞菁(VOPc)与钒酞菁(VPc)分子的扫描隧道显微镜图像模拟

利用第一性原理方法模拟了自由钒氧酞菁(VOPc)和钒酞菁(VPc)分子的扫描隧道显微镜(STM)图像,与实验观察结果相当符合.理论STM图像都显示出亚分子内结构,外围呈四叶状.其主要差异表现在VOPc分子中心处的钒氧离子在STM图像中为一空洞,而在VPc分子的STM图像中钒离子为突起的亮斑.通过分析VOPc和VPc分子的电子结构,对模拟结果给出自洽的理论解释.造成两者图像显著不同的物理原因是VPc分子在费米能级附近有明显含dz2成分的分子轨道,导致钒离子在STM图像中央为突起的亮斑.而在VOPc分子中dz2分态密度峰位由于氧原子的加入使之远离费米能级,使STM不能“看到”VOPc分子中钒氧离子. 关键词： 钒氧酞菁 钒酞菁 STM图像模拟 电子结构     

自旋轨道耦合Su-Schrieffer-Heeger原子链系统的电子输运特性

在Su-Schrieffer-Heeger (SSH)原子链中,电子在胞内和胞间的跳跃依赖于其自旋时,即SSH原子链存在自旋轨道耦合作用时,存在不同缠绕数的非平庸拓扑边缘态.如何探测自旋轨道耦合SSH原子链不同缠绕数的边缘态是一个重要问题.本文在紧束缚近似下研究了自旋轨道耦合SSH原子链的非平庸拓扑边缘态性质及其零能附近的电子输运特性.研究发现四重和二重简并边缘态的缠绕数分别为2和1;并且仅当源极入射电子的自旋被极化(铁磁电极)时,自旋轨道耦合SSH原子链在零能附近的电子输运特性才能反映其边缘态的能谱特性.尤其是,随着自旋轨道耦合SSH原子链与左、右导线之间的耦合强度由弱到强改变,对于缠绕数为2的四重简并边缘态,入射电子在零能附近的透射峰数目将从4个变为0;而对于缠绕数为1的二重简并边缘态情形,其透射峰数目将从2个变为0.因此,在源极为铁磁电极的情形下,通过观察自旋轨道耦合SSH原子链在零能附近电子共振透射峰的数目随着其与左、右导线之间耦合强度的变化,来探测其不同缠绕数的边缘态.上述结果为基于电子输运特性探测自旋轨道耦合SSH原子链不同拓扑性质的边缘态提供了一种可选择的理论方案.     

TiO_2缺陷结构电子性质的第一性原理计算

本文采用第一性原理研究了O空位缺陷、Ti空位缺陷TiO_2的能带结构、总态密度、吸收谱.通过研究发现:与TiO_2超胞结构的能带相比,O空位缺陷体系的价带与导带能量均向低能区域移动,费米能级与导带底交错,呈现出n型半导体,Ti空位缺陷的TiO_2的费米能级与价带顶部的能级交错,为p型半导体材料.对于O空位缺陷TiO_2总态密度与分波态密度在低能区的态密度则主要由O的3s、3p轨道贡献的能量,而在费米能附近的态密度则主要由Ti的4d轨道贡献能量;Ti空位缺陷的态密度总态密度仍然由O的3s、3p和Ti的4d轨道贡献的能量;同时分析吸收光谱发现峰值下移较多的是钛缺陷体系,其原因在于Ti缺陷结构中未成键电子的相互作用.     

K_2AgF_4和Cs_2AgF_4的电子结构和磁性（英文）

采用第一性原理计算我们研究了Jahn-Teller(JT)畸变诱导下K2AgF4和Cs2AgF4中的轨道有序和磁性.K2AgF4的基态是层内反铁磁态(AFM2),此时最近邻的Ag2+磁矩互为反平行,而它们的轨道则是相互平行的.Cs2AgF2+4的基态是层间反铁磁态(AFM1),同一AgF2层中的Ag2+磁矩相互平行,与近邻的AgF2层中Ag磁矩互为反平行.这两种体系磁性基态都可以用Goodenough-Kanamori规则进行很好的解释.     

Heusler合金Ni_2MnGa马氏体相变微观电子结构机理的研究

采用基于密度泛函理论的第一性原理框架下的投影扩充波函数(PAW)方法,研究了Heusler合金Ni2Mn Ga马氏体相变的微观电子结构机理.结果表明:Ni2Mn Ga发生马氏体相变时,其晶体发生了自正八面体结构朝z轴拉长型八面体结构的畸变.此畸变源自于由Ni的eg轨道电子的非均匀排布所引发的强带Jahn–Teller效应,其发生的机制是:通过孤对电子由dx2-y2轨道转移到dz2轨道,导致x、y方向的配体内移,z方向的配体外移,从而使dx2-y2、dxy能级升高,及dz2、dyz、dxz能级降低,消除和降低能级的简并度,体系能量降低,体系畸变到一个更稳定的状态(马氏体相).     

BaTi2As2O电子结构的第一性原理研究

利用基于密度泛函理论的平面波赝势方法,研究BaTi2As2O的能带结构、费米面和态密度.发现:BaTi2As2O是一种非磁性金属,费米能级处的态密度主要来自Ti原子的3d电子,Ti 3d轨道和As 4p轨道有较强的杂化.没有发现其磁性基态,说明Ti原子上没有局域磁矩,与Pickett对Na2Ti2Sb2O的研究结论相吻合.     

BaCrSi4O10与AgGaSe2:Cr2+吸收光谱的精细结构及自旋单态对零场分裂参量的影响

在强场图像中构造了四角对称环境中Cr²⁺离子包括自旋单态在内的完全能量矩阵, 通过对角化能量矩阵方法, 计算得到了BaCrSi₄O₁₀与AgGaSe₂:Cr²⁺吸收光谱的精细结构及自旋单态对零场分裂参量的影响. 从理论上给出了BaCrSi₄O₁₀与AgGaSe₂:Cr²⁺吸收光谱的精细结构及BaCrSi₄O₁₀的零场分裂参量值. 计算结果显示自旋单态对零场分裂参量D的影响完全可忽略, 但对a和F的影响比较大. 这种影响主要来自自旋-轨道耦合导致的自旋五重态与自旋三重态和自旋单态的相互作用, 而自旋轨道耦合的选择定则显示自旋单态并非直接影响五重态而是通过自旋三重态间接地影响基态的五重态. 因此, 为了得到准确的零场分裂参量值, 所有的自旋态都应该考虑.     

钒氧卟啉正负离子的结构畸变与电子-振动耦合的DFT研究

用PBE1PBE方法研究了钒氧卟啉一价阴离子([VOP]^-)、一价阳离子([VOP]⁺)的单态和三重态结构. 结果表明[VOP]^-和[VOP]⁺的最稳定电子态均为三重态,其未配对电子一个占据钒的d_xy轨道,另一个占据卟啉环的π轨道,因此两者均为π-自由基. 中性分子(VOP)的双重态最稳定,其未配对电子占据钒的d_xy轨道. 双重态VOP具有较高的C_4v对称性,而三重态[VOP]^- 离子由于发生姜-泰勒效应对称性降低为C_2v. 计算了[VOP]^-姜-泰勒活性振动模式的电子-振动耦合常数,并用前线KS轨道的节面分布解释了姜-泰勒畸变沿特定简正模式发生的原因. 三重态[VOP]⁺ 阳离子的卟啉环发生键长交替变化,构型畸变起源于电子态近简并引起的赝姜-泰勒效应,导致其对称性从C_4v降低为C₄,其结构变化可以用重组的前线KS轨道的节面分布解释.     

Crossing the gap from p- to n-type doping: nature of the states near the chemical potential in La(2)-(x)Sr(x)CuO(4) and Nd(2-x)Ce(x)CuO(4-delta)

We report on an x-ray absorption and resonant photoemission study on single crystals of the high-T(c) cuprates La2-xSrxCuO4 and Nd(2-x)Ce(x)CuO(4-delta). Using an intrinsic energy reference, we find that the chemical potential of La2-xSrxCuO4 lies near the top of the La2CuO4 valence band whereas in Nd(2-x)Ce(x)CuO(4-delta) it is situated near the bottom of the Nd2CuO4 conduction band. The data clearly establish that the introduction of Ce in Nd2CuO4 results in electrons being doped into the CuO2 planes. We infer that the states closest to the chemical potential have a Cu 3d(10) singlet origin in Nd(2-x)Ce(x)CuO(4-delta) and a 3d(9)L singlet origin in La2-xSrxCuO4.     

Ferromagnetism induced by orbital order in the charge-transfer insulator Cs2AgF4: an electronic structure study

Cs2AgF4 was proposed to be an orbitally ordered ferromagnet based on recent neutron scattering data. Here, we report a detailed electronic structure study within the local spin density approximation also including strong Coulomb repulsion U. We investigate the influence of an orthorhombic distortion of the Ag environment and the importance of the on-site Coulomb repulsion. We find good quantitative agreement with both the experimentally observed exchange coupling and structural changes. Thus, our results strongly support that Cs2AgF4 is a strongly correlated charge-transfer insulator where the ferromagnetism is driven by orbital order.     

高Tc氧化物超导体的电子结构

本文综述了高Tc氧化物超导体(La_2CuO_4及YBa_2Cu_3O_(7-8)的(计算)电子结构。本文基于Freeman教授研究组的工作。 (1) 体心四方结构的La_2CuO_4能带结构计算结果表明:La_2CuO_4的电子结构由在正方形Cu-O平面内的Cu3d-O2p相瓦作用所控制。存在一个沿[110]方向|q|=2k_F(强的)迭套的Fermi表面,它导致了电子驱动的结构失稳,以及在电子状态密度上的VanHove对数奇性。此种Fermi面的迭套被认为是引起了(Peierls 2k_F)失稳性,从而解释了La_(2-x)M_xCuO_4由四方结构到正交结构的相变。 (2) 如同在La_(2-x)M_xCuO_4中的情况一样,具正交结构的YBa_2Cu_3O_(7-8)的电子结构由Cu-O间的相互作用所支配;同时存在着二维及一维的Cu3d-O2p相互作用为YBa_2Cu_3O_(7-8)电子结构的特征。YBa2Cu_3O_(7-8)在E_F处的状态密度值低于La_(2-x)M_xCuO_4的相应值,在YBa_2Cu_3O_(7-8)中的Y或Ba原子作用如同一电子的施主。     

一些高Tc超导体的弹性性质

 本文用超声相比较方法测定了高T_c超导体La_1.85Sr_0.15CuO₄，La₂CuO₄和YBa₂Cu₃O₇的纵波和横波声速，进而导出了它们的纵向模量、切变模量、杨氏模量、泊松比、德拜温度及定体比热。在La_1.85Sr_0.15CuO₄样品上，还进行了压力实验，发现所有弹性模量都是随压强增加而增加。定体比热c_V和泊松比σ在高压下则略有下降。德拜温度是随压强增加而增加的。     

CuO/Al2O3、CuO/CeO2-Al2O3和CuO/La2O3-Al2O3催化剂中CuO物种被CO氧化的比较

用浸渍法制备了CuO/Al2O3 (Cu/Al)、CuO/CeO2- Al2O3 (Cu/CeAl)和CuO/La2O3-Al2O3(Cu/LaAl)催化剂. 通过原位XRD、Raman和H2-TPR方法， 对催化剂中的CuO物种以及CuO-Al2O3的固-固相反应进行了表征. 结果表明，对于Cu/Al催化剂，CuAl2O4存在于CuO与Al2O3层之间，CuO以高分散和晶相两种相态存在于催化剂的表层；对于Cu/CeAl催化剂，除了少量高分散和晶相的CuO存在于表层外，大部分CuO迁移到了CeO2的内层，     

Magnon heat transport in doped La2CuO4

We present results of the thermal conductivity of La2CuO4 and La(1.8)Eu(0.2)CuO4 single crystals which represent model systems for the two-dimensional spin-1/2 Heisenberg antiferromagnet on a square lattice. We find large anisotropies of the thermal conductivity which are explained in terms of two-dimensional heat conduction by magnons within the CuO2 planes. Nonmagnetic Zn substituted for Cu gradually suppresses this magnon thermal conductivity kappa(mag). A semiclassical analysis of kappa(mag) is shown to yield a magnon mean free path which scales linearly with the reciprocal concentration of Zn ions.     

Muon spin relaxation studies of magnetic-field-induced effects in high-Tc superconductors

Muon spin relaxation measurements in high transverse magnetic fields [FORMULA: SEE TEXT] revealed strong field-induced quasistatic magnetism in the underdoped and Eu-doped (La,Sr)2CuO4 and La1.875Ba0.125CuO4, existing well above Tc and TN. The susceptibility counterpart of Cu spin polarization, derived from the muon spin relaxation rate, exhibits a divergent behavior towards T approximately 25 K. No field-induced magnetism was detected in overdoped La1.81Sr0.19CuO4, optimally doped Bi2212, and Zn-doped YBa2Cu3O7.     

Evidence for suppressed screening on the surface of high temperature La(2-x)SrxCuO4 and Nd2(2-x)CexCuO4 superconductors

Hard x-ray photoemission spectroscopy (PES) of Cu core electronic states, with a probing depth of approximately 60 A, is used to show that the Zhang-Rice singlet feature is present in La2CuO4 but is absent in Nd2CuO4. Hole and electron doping in La(2-x)SrxCuO4 (LSCO) and Nd(2-x)CexCuO4 (NCCO) result in new well-screened features which are missing in soft x-ray PES. Impurity Anderson model calculations establish screening from doped states as its origin, which is strongly suppressed within 15 A of the surface. Complemented with x-ray absorption spectroscopy, the small chemical-potential shift in core levels (approximately 0.2 eV) are shown to be consistent with modifications of valence and conduction band states spanning the band gap (approximately 1 eV) upon hole and electron doping in LSCO and NCCO.     

Two-dimensional superconducting fluctuations in stripe-ordered La1.875Ba0.125CuO4

Recent spectroscopic observations of a d-wave-like gap in stripe-ordered La(2-x)Ba(x)CuO(4) with x=1/8 have led us to critically analyze the anisotropic transport and magnetization properties of this material. The data suggest that concomitant with the spin ordering is an electronic decoupling of the CuO(2) planes. We observe a transition (or crossover) to a state of two-dimensional (2D) fluctuating superconductivity, which eventually reaches a 2D superconducting state below a Berezinskii-Kosterlitz-Thouless transition. Thus, it appears that the stripe order in La(2-x)Ba(x)CuO(4) frustrates three-dimensional superconducting phase order, but is fully compatible with 2D superconductivity and an enhanced T(c).     

Effect of disorder outside the CuO2 planes on Tc of copper oxide superconductors

The effect of disorder on the superconducting transition temperature T(c) of cuprate superconductors is examined. Disorder is introduced into the cation sites in the plane adjacent to the CuO2 planes of two single-layer systems, Bi(2.0)Sr(1.6)Ln(0.4)CuO(6+delta) and La(1.85-y)Nd(y)Sr0.15CuO4. Disorder is controlled by changing rare earth (Ln) ions with a different ionic radius in the former, and by varying the Nd content in the latter with the doped carrier density kept constant. We show that this type of disorder works as weak scatterers in contrast to the in-plane disorder produced by Zn, but remarkably reduces T(c), suggesting novel effects of disorder on high-T(c) superconductivity.