Fe(Ⅱ)-N_4S_2自旋翻转单分子磁体的电子输运性质（英文）

由于其具有高自旋和低自旋磁性双稳态特性,单分子磁体是构建分子自旋电子器件最有潜力的候选体系.基于第一性原理计算和非平衡格林函数方法,我们研究了Fe(Ⅱ)-N_4S_2自旋翻转单分子磁体在两个金电极之间的电子结构和输运特性.优化的几何结构参数和计算出来的磁性与实验结果吻合,基于翻转能垒,发现该磁体在可见光范围可实现高低自旋之间的翻转.当磁体处于高自旋态时,其电流在小偏压条件下主要由自旋向下的电子贡献,表现出显著的自旋过滤效应.这些理论研究结果表明此类单分子磁体可用设计分子自旋电子学器件.     

二维NiBr2单层自旋电子输运以及光电性质

磁性半导体材料在自旋电子器件领域具有重要的应用前景.本文设计了一些基于磁性半导体NiBr₂单层的纳米器件结构,并采用密度泛函理论结合非平衡格林函数方法,研究了其自旋输运和光电性质.结果表明,在不同的输运方向(扶手椅形和锯齿形),NiBr₂单层PN结二极管表现出明显的整流效应及自旋过滤效应,这两种效应在其亚3 nm PIN结场效应晶体管中也同样存在.NiBr₂单层PIN结场效应晶体管的电子传输受到栅极电压的调控,电流随着栅极电压的增大受到抑制.另外,NiBr₂单层对蓝、绿光有较强的响应,其光电晶体管在两种可见光的照射下可以产生较强的光电流.本文研究结果揭示了NiBr₂单层的多功能特性,为镍基二卤化物在半导体自旋电子器件和光电器件领域的应用提供了重要参考.     

异氰酸分子NH(a1Δ)+CO(X1Σ+)通道在193nm的离子成像光解动力学研究

The photodissociation dynamics of isocyanic acid (HNCO) has been studied by the timesliced velocity map ion imaging technique at 193 nm. The NH(a¹Δ) products were measured via (2+1) resonance enhanced multiphoton ionization. Images have been accumulated for the NH(a¹Δ) rotational states in the ground and vibrational excited state (v=0 and 1). The center-of-mass translational energy distribution derived from the NH(a¹Δ) images implies that the CO vibrational distributions are inverted for most of the measured ¹NH(v|j) internal states. The anisotropic product angular distribution observed indicates a rapid dissociation process for the N-C bond cleavage. A bimodal rotational state distribution of CO(v) has been observed, this result implies that isocyanic acid dissociates in the S₁ state in two different pathways.     

AlC分子 X4∑-和B4∑-电子态的光谱性质

采用Davidson修正的内收缩多参考组态相互作用方法(MRCI+Q) 结合Dunning等的相关一致基aug-cc-pVnZ (n=D,T,Q,5,6) 计算了AlC分子X⁴∑^-和B⁴∑^-态的势能曲线, 并利用总能量外推公式将这两个态的总能量分别外推至完全基组极限. 对势能曲线进行核价相关修正及相对论修正, 并详细讨论了基组、核价相关和相对论修正 等对X⁴∑^-和B⁴∑^-电子态的能量和光谱常数的影响. 拟合核价相关及相对论效应修正的外推势能曲线, 得到了AlC分子X⁴∑^- 和B⁴∑^-电子态的主要光谱常数T_e, R_e, ω_e, ω_ex_e, ω_ey_e, B_e和α_e. 它们与实验结果符合较好. 求解双原子分子核运动的径向Schrödinger方程, 找到了无转动的AlC分子两个电子态的全部振动态. 针对每一振动态, 还分别计算了其相应的振动能级和惯性转动常数等分子常数. 它们与已有的实验结果一致. 关键词： 光谱常数 分子常数 核价相关修正 相对论修正     

O2分子吸附的金属表面的O2(1Δg)猝灭

建立了一套流动装置测量单重态氧O₂(¹Δ_g)在O₂分子吸附的金属Cu、Cr、Ni和Ag表面的猝灭几率. 随实验时间和O₂(¹Δ_g)浓度增加,猝灭几率增加. 当上述金属样品在几帕斯卡的真空度下暴露数小时后猝灭几率会回到原先水平. 提出了一种基于表面吸附位上弱化学吸附的表面吸附氧分子O₂(¹∑_{g相似文献}   

自旋转换配合物[Fe（C4H4N2）｛Pt（CN4）｝]晶体结构及低温相的研究

本文对自旋转换配合物[Fe(C4H4N2){Pt(CN4)}]进行了晶体结构的理论研究,分析表明XRD测量给出的结构只是一个理想化的结构,不适用于理论计算.我们通过第一性原理计算给出的晶格结构空间群为P2/m,相比较XRD的理想结构的空间群P4/m,其对称性降低,该体系实际属于单斜晶系,而不是测量中所给出的四方晶系的结构.通过对比实验数据特别是对低温相的分析,看出对该配合物的理论计算得出的结构常数及键长与实验数据相吻合.用局域密度近似和广义梯度近似算得的低温相的能量分裂分别为2.7824eV和2.5617eV,故低自旋态为低温相的稳态,这也与实验结论很好的吻合.     

O2分子激发态a1Δg和b1Σ+g态的分析势能函数

以aug-cc-pVQZ,cc-pV5Z,6-311++g（d,p）和6-311++g（3df,3pd）等为基函数,采用多组态相互作用（MRCI）方法对O₂分子最低的两个激发态¹Δ_g和¹Σ⁺_g的平衡结构、谐振频率和势能曲线进行了计算.并选用Murrell-Sorbie势能函数对曲线进行拟合,利用拟合的参数值计算出了力常数和光谱数据.结果表明计算值与实验值符合较好. 关键词： MRCI 势能函数 力常数 光谱数据     

BeH2(X1Σ+g)与H2S(X1A1)分子的结构与解析势能函数

运用单双取代二次组态相关(QCISD)方法,在6-311++G(3df,3pd)基组水平上,对BeH₂和H₂S分子的结构进行了优化计算,得到基态BeH₂分子的稳定结构为D_∞h构型,电子态为X¹Σ⁺_g,平衡核间距R_BeH=0.13268nm,R_{关键词： 2}')" href="#">BeH₂ 2S')" href="#">H₂S Murrell-Sorbie函数 多体项展式理论 解析势能函数     

Eu3+掺杂Gd2W2O9和Gd2（WO4）3纳米荧光粉发光性质研究

采用共沉淀法制备了不同Eu3+掺杂浓度的Gd2W2O9和Gd2(WO4)3纳米发光材料.通过对纳米材料样品的X射线衍射谱(XRD)和场发射扫描电镜(FE-SEM)照片的观察和分析,对样品的结构和形貌进行了表征.测量了各样品的发射光谱、激发光谱,计算了各样品的部分J-O参数和Eu3+5D0能级量子效率,绘制了不同基质中Eu3+发光的浓度猝灭曲线,对Eu3+掺杂的Gd2W2O9和Gd2(WO4)3纳米发光材料的光致发光性质进行了研究.实验结果证明,与较常见的Gd2(WO4)3:Eu一样,Gd2W2O9:Eu中Eu3+5D0→7F2跃迁的红色发光也能被395nm和465nm激发光有效激发,具有近紫外(蓝光)相对激发效率高,猝灭浓度大的优点,有潜力成为高效的近紫外(蓝光)激发白光LED用红色荧光粉材料.     

非线性光学晶体HgGa2S4 和 Hg0.5Cd0.5Ga2S4的能带结构、化学键及光学性质研究

用密度泛函理论和非谐振子模型计算了晶体HgGa₂S₄和Hg_0.5Cd_0.5Ga₂S₄的能带结构、态密度、化学成键及线性、非线性光学性质。结果表明：HgGa₂S₄的价带顶部主要是Ga-S成键态的贡献，导带底部主要是Ga-S反键态的贡献; Hg_0.5Cd_0.5Ga₂S₄的价带顶部主要由S-3p轨道组成，导带底部主要是Ga-S反键态的贡献。布居分析表明Ga-S键主要是共价成分，而Hg-S和Cd-S键主要是离子成分。HgGa₂S₄的折射率计算值与实验值在低能量区很好吻合。另外，HgGa₂S₄的能隙计算值比Hg_0.5Cd_0.5Ga₂S₄小，而二阶非线性极化率比Hg_0.5Cd_0.5Ga₂S₄大。     

六配位FeN6自旋翻转化合物的自旋输运特性

本文采用第一性原理计算和非平衡格林函数方法,研究了六配位FeN₆的自旋输运特性. 理论计算结果表明在外场(如光辐射)作用下通过改变配体与磁芯间键长来实现磁体的高低自旋之间的转换. 基于计算得到的透射谱和伏安曲线,发现通过高自旋态分子结的电流显著大于低自旋态磁体,且通过高自旋态分子结的输运特性由自旋向下的电子提供主要贡献. 理论预测出来的分子开关和自旋过滤效应表明此类铁基六配体自旋翻转化合物可用于分子自旋电子学器件设计.     

Electronic states of lanthanide in the ternary thiogallate CaGa2S4

The electronic states of lanthanide (Ln) doped CaGa₂S₄ are investigated by the molecular orbital calculations for a spherical cluster of LnCa₈Ga₁₂S₂₄ using the FORTRAN program DVSCAT on the basis of the Discrete Variational method with Xα potentials (DV-Xα). In view of the SCF convergence, the Ln-doped lattice should contract to 85-90% of the mother crystal around the Ln atom for the lightweight lanthanides from Ce to Sm. On the other hand, the lattice contraction is very small for the heavyweight lanthanides, especially for Er, Tm and Yb in contrast to the generally known lanthanide contraction for Ln³⁺ ions. This is probably attributed to the effective charges of Ln atoms calculated here to be less than +1 for all lanthanides contrary to the chemically accepted value of +3. The energy level scheme of 4f and 5d related molecular orbitals is proposed for each Ln substituting Ca in CaGa₂S₄, showing that the optical processes relating to the 5d→4f transition must be complicated especially for the lightweight Ln-doped CaGa₂S₄.     

Electronic structure and optical properties of Sb2S3 crystal

The electronic and optical properties of Sb₂S₃ are studied using the full potential linearized augmented plane wave (FP-LAPW) method as implemented in Wien2k. In this approach, the alternative form of the generalized gradient approximation (GGA) proposed by Engel and Vosko (EV-GGA) was used for the exchange correlation potential. The calculated band structure shows a direct band gap. The contribution of different bands was analyzed from total and partial density of states curves. Moreover, the optical properties, including the dielectric function, absorption spectrum, refractive index, extinction coefficient, reflectivity and energy-loss spectrum are all obtained and analyzed in detail.     

Electronic structure of HgGa2S4

The electronic structure and chemical bonding in HgGa₂S₄ crystals grown by vapor transport method are investigated with X-ray photoemission spectroscopy. The valence band of HgGa₂S₄ is found to be formed by splitted S 3p and Hg 6s states at binding energies BE=3-7 eV and the components at BE=7-11 eV generated by the hybridization of S 3s and Ga 4s states with a strong contribution from the Hg 5d states. At higher binding energies the emission lines related to the Hg 4f, Ga 3p, S 2p, S 2s, Hg 4d, Ga LMM, Ga 3p and S LMM states are analyzed in the photoemission spectrum. The measured core level binding energies are compared with those of HgS, GaS, AgGaS₂ and SrGa₂S₄ compounds. The valence band spectrum proves to be independent on the technological conditions of crystal growth. In contrast to the valence band spectrum, the distribution of electron states in the bandgap of HgGa₂S₄ crystals is found to be strongly dependent upon the technological conditions of crystal growth as demonstrated by the photoluminescence analysis.     

Structural and Electronic Properties of Li2Mg(NH)2 for Hydrogen Storage: First-principles Study

应用第一原理方法研究了储氢材料α-Li₂Mg(NH)₂和β-Li₂Mg(NH)₂两种构型的结构性质和电子性质．计算优化得到的晶胞参数和N-H键长符合实验得到的数据．通过Murnaghan状态方程得到了体积模量和零压力下的能量,计算结果表明α-Li₂Mg(NH)₂为基态构型．通过Mulliken布居分析说明α构型的N-Li/Mg的离子特性和N-H间的交互作用都弱于β构型．态密度分析结果表明,价带轨道主要由N原子的s轨道和p轨道占据,并与H原子的s轨道杂化．     

First-principles calculations of electronic, optical and elastic properties of ZnAl2S4 and ZnGa2O4

The optimized crystal structures, band structures, partial and total densities of states (DOS), dielectric functions, refractive indexes and elastic constants for ZnAl₂S₄ and ZnGa₂O₄ were calculated using the CASTEP module of Materials Studio package. Pressure effects were modeled by performing these calculations for different values of external hydrostatic pressure up to 50 GPa. Obtained dependencies of the unit cell volume on pressure were fitted by the Murnaghan equation of state, and the relative changes of different chemical bond lengths were approximated by quadratic functions of pressure. Variations of applied pressure were shown to produce considerable re-distribution of the electron densities around ions in both crystals, which is evidenced in different trends for the effective Mulliken charges of the constituting ions and changes of contour plots of the charge densities. The longitudinal and transverse sound velocities and Debye temperatures for both compounds were also estimated using the calculated elastic constants.     

Electronic structure of non-centrosymmetric AgCd2GaS4 and AgCd2GaSe4 single crystals

X-ray photoelectron core-level and valence-band spectra for pristine and Ar⁺-ion irradiated (0 0 1) surfaces of AgCd₂GaS₄ and AgCd₂GaSe₄ single crystals grown, respectively, by the Bridgman method and the method of direct crystallization have been measured in the present work. The X-ray photoelectron spectroscopy (XPS) results reveal high chemical stability of (0 0 1) surfaces of AgCd₂GaS₄ and AgCd₂GaSe₄ single crystals. Electronic structure of AgCd₂GaS₄ has been calculated employing the full potential linearized augmented plane wave method. For the AgCd₂GaS₄ compound, the X-ray emission bands representing the energy distribution of the valence Ag d-, Cd d-, Ga p- and S p-like states were recorded and compared on a common energy scale with the XPS valence-band spectrum. The theoretical and experimental data regarding the occupation of the valence band of AgCd₂GaS₄ were found to be in excellent agreement to each other. Second harmonic generation (SHG) efficiency of AgCd₂GaS₄ by using the 320 ns CO laser at 5.5 μm has been recorded within the temperature range 80–300 K. Substantial increase of the photoinduced SHG which in turn is substantially dependent on the temperature has been detected for the AgCd₂GaS₄ compound.     

Ab initio study of structural, electronic and optical properties of MnHg(SCN)4 and FeHg(SCN)4

 The structural, electronic and optical properties of MnHg(SCN)₄ and FeHg(SCN)₄ were studied by means of quantum-mechanical calculations based on the density-functional theory and pseudopotential method. The lattice constants can be compared with the experimental values when the effects of temperature are considered. The peaks of partial density of states of S, C, N and Hg of FeHg(SCN)₄ have a tendency of shifting to the higher energy levels relative to those of MnHg(SCN)₄. The distributions of the 3d electronic states in the transition metal atoms show quite large difference and decide different optical properties. We found that absorptional peaks of FeHg(SCN)₄ lag behind those of MnHg(SCN)₄ and the peak in the infrared range has a higher absorptional intensity, which are in accord with the experimental results. By analyzing the distributions and transitions of the 3d electronic states, we explained the different absorption phenomena.     

Electronic structure of ZrTiO4 and HfTiO4: Self-consistent cluster calculations and X-ray spectroscopy studies

Total and partial densities of states of the constituent atoms of ZrTiO₄ and HfTiO₄ titanates have been calculated using a self-consistent cluster method as incorporated in the FEFF8 code. The calculations reveal the similarity of the electronic structure of both titanates and indicate that the valence band of the compounds under consideration is dominated by contributions of O 2p states. These states contribute throughout the whole valence-band region; however their maximum contributions occur in the upper portion of the band. Other significant contributors in the valence-band region are Ti 3d and Zr 4d states in ZrTiO₄ and Ti 3d and Hf 5d states in HfTiO₄. All the above d-like states contribute throughout the whole valence-band region of the titanates; however maximum contributions of the Ti 3d states occur in the upper portion, whilst those of the Zr 4d (Hf 5d) states are in the central portions of the valence band. The FEFF8 calculations render that the bottom of the conduction band of ZrTiO₄ and HfTiO₄ is dominated by contributions of Ti 3d^? states, with also smaller contributions of Zr 4d^?/Hf 5d^? and O 2p^? states. To verify the above FEFF8 data, the X-ray emission bands, representing the energy distributions of mainly O 2p, Ti 3d and Zr 4d states, were measured and compared on a common energy scale. These experimental data are found to be in agreement with the theoretical FEFF8 results for the electronic structure of ZrTiO₄ and HfTiO₄ titanates. Additionally, X-ray photoelectron valence-band and core-level spectra were recorded for the constituent atoms of the titanates under study.