One - determinantal pure state versus ensemble Kohn-Sham solutions in the case of strong electron correlation: CH2 and C2

The possibility that the Kohn-Sham (KS) solution for a noninteracting auxiliary electron system is not the conventional one-determinantal pure state but a few-determinantal ensemble has been investigated. The KS solutions (the exchange-correlation potential v _xc and the orbitals) have not been approximated by local-density or density-gradient approximations but have been constructed from an accurate ab initio electron density. The lowest singlet states of the CH₂ and C₂ molecules have been selected for this investigation since for these cases the ground-state wave function Ψ is nondegenerate but has an essentially multideterminantal character (electron correlation is strong). For C₂ the dependence of the type of KS solution on the bond distance R(C–C) has been studied at the QZ level. For the shortest distance considered, R(C–C)=1.8 a.u., a pure-state KS solution has been obtained. For the equilibrium distance R _e(C–C)=2.348 a.u. and at larger distances ensemble solutions have been obtained with widely varying weights of the individual determinants, depending on the bond distance. For CH₂ the dependence of the type of KS solution on the basis has been studied: calculation in the triple zeta (TZ) basis for the KS orbitals yields an ensemble solution, while the pure-state KS solution has been obtained in the quadruple zeta (QZ) basis. The form of the KS orbitals has been compared with that of the natural orbitals (NOs). It has been shown for the model example of the stretched H₂ molecule as well as for CH₂ and C₂, that the KS orbitals of the pure state may be rather different from the corresponding NOs, while the occupied KS orbitals of the ensemble solution can be considered as plausible approximations to the corresponding NOs. Received: 10 February 1998 / Accepted: 10 June 1998 / Published online: 3 September 1998     

Ab Initio Modeling of Interatomic Interactions in 3C–SiC:M, M = Cr, Mn, Fe, Co

The electronic structure and chemical binding parameters of impurity atoms M = Cr, Mn, Fe, Co in cubic silicon carbide are considered in DFT (density functional theory) and X-DV (discrete variation) approximations. A scheme for calculating the binding energies in the cluster approach is suggested. Stoichiometric and superstoichiometric models of impurity incorporation are investigated. The binding energy is higher for the stoichiometric model. In the superstoichiometric model, the titanium and iron atoms preferably occupy the Si₄ interstice. For all other atoms, the MSi, Sii model is preferable. The incorporated impurity weakens the basic Si–C bonds.     

Origin of the chemical shift in X‐ray absorption near‐edge spectroscopy at the Mn K‐edge in manganese oxide compounds

The absorption edge in Mn K‐edge X‐ray absorption spectra of manganese oxide compounds shows a shift of several electronvolts in going from MnO through LaMnO₃ to CaMnO₃. On the other hand, in X‐ray photoelectron spectra much smaller shifts are observed. To identify the mechanisms that cause the observed chemical shifts, 1s ionization as well as 1s → “4p” transition energies have been determined by electronic structure calculations on embedded Mn ions and embedded MnO₆ clusters. Systematic variation of the cluster geometry and the cluster embedding showed that the chemical shifts are predominantly determined by two effects: the changes in the Mn 3d occupation and the changes in the Madelung potential. The large chemical shift in the 1s → 4p transition energies between different materials occurs because the two effects do not compensate each other. The chemical shifts obtained for the embedded MnO₆ clusters agree reasonably with the experimental shifts. The small sensitivity to the material observed for the Mn 1s ionization energies is explained by the near cancellation of the effects of the Madelung potential and the 3d occupation of the Mn ion. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

The influence of composition and fine structure on a thermographical characteristics of micas

Several isomorphic groups of micas: Muscovite-Phengite-Muscovite-Li-Muscovite; Biotite-Zinnwaldite-Lepidolite and Biotite-Phlogopite were investigated by DTA, TG and DTG. Octehedral vacancies and the sites of octahedral cationic occupancy were determined from IR-spectra of the hydroxyls. The influence of a composition and fine structure of the micas on the shape of the thermal curves was discussed. A one to one correspondence between the isomorphic series members and individual thermal curves makes it possible to determine the chemical composition of a mica sample. The combination of thermal and IR-spectra of hydroxyl analyses permits to link the Order-Disorder data with thermal properties of mica. Dedicated to Professor Lisa Heller-Kallai on the occasion of her 65^th birthday     

Ce3+激活NaSr4(BO3)3荧光粉的格位占据和发光性质研究

采用高温固相法制备了一系列可被紫外光有效激发的Na_1+xSr_4-2x(BO₃)₃∶xCe³⁺荧光粉,并通过X射线衍射、扫描电镜、荧光光谱等测试方法对样品的物相结构、形貌和发光特性进行了表征及分析。X 射线衍射结果显示,Ce³⁺成功掺入到基质NaSr₄(BO₃)₃中;利用高斯峰拟合、多光谱对比等手段,分析并验证了发光中心Ce³⁺占据了NaSr₄(BO₃)₃中Sr²⁺(1)和Sr²⁺(2)两个格位;研究了不同浓度Ce³⁺的掺杂对发光位置和发光强度的影响,随着Ce³⁺掺杂浓度的提高,发射光谱出现红移,发光强度出现增强→减弱→再增强的趋势;将荧光粉的发射光谱与植物光合色素吸收光谱进行对比,发现它不仅可以吸收300~350 nm的紫外光,发射光谱还很好地覆盖了植物光合色素所需的蓝光区吸收波段,证明其在农业生产的转光剂方面有潜在应用价值。     

海峡两岸职业安全卫生法制比较

职业安全卫生法是劳动基准法的重要组成部分,并因其涉及面广、内容庞杂而渐自成体系.由于法制背景的不同,两岸的职业安全卫生立法在体例结构、适用范围以及具体制度内容等方面存在诸多差异.在当前,两岸事实上面临着同样的问题,即要将先进理念与现行立法相结合,从根本上带动整个职业安全卫生立法的革新.     

经济发达城市劳动力市场分割维度的实证研究

借用CGSS开放数据库中部分沿海地区的城市调查数据,使用方差分析、回归分析等分析方法研究中国沿海经济发达城市中劳动力市场分割的表现维度。研究结果表明,沿海发达城市的劳动力市场分割在单位性质、行业和职业层面都有不同程度的存在,其中,职业层面的劳动力市场分割的程度最严重,其次是单位性质层面也存在一定程度的劳动力市场分割,在行业层面的劳动力市场分割的程度最低,但在统计上也是显著的。     

日据时期的台湾天主教静修女中

综合中、西文史料和前人的著述,对台北静修女中成立、发展的历史进行了梳理和评析,认为日据时期的台北静修女中,培养了一大批具有职业意识的近代女性,为保存汉文化和民族意识发挥了作用。     

The multifractal analysis of the occupation measure of a Lévy process

We introduce the results on the multifractal structure of the occupation measures of a Brownian Motion, a stable process, a general subordinator and a stochastic process derived from random reordering of the Cantor set. We also introduced an interesting and powerful technique to investigate the multifractal spectrum. Foundation item: Supported by the National Natural Science Foundation of China Biography: Hu Xiao-yu (1964-), female, Professor, research interest: probability theory, random fractals.     

模具专业毕业设计必须与企业生产相结合

阐明职业教学，毕业设计与企业生产实践相结合的重要性，分析以往毕业设计误区，介绍毕业设计与企业生产实践相结合具体做法，收获与体会