Electronic band structure matching for half- and full-Heusler alloys

We explore the lattice and the electronic band structures matching between the half-metallic Heusler alloys (half-Heusler NiMnSb and full-Heusler Co₂MnSi) and several hypothetical non-magnetic Heusler alloys by using first principle calculations. The lattice and band structure matching are almost perfectly satisfied between the two materials of similar crystal structures: (i) NiMnSb and XYSb and (ii) Co₂MnSi and X₂YSi, where X, Y=Ni or Cu. Owing to the high interface spin scattering asymmetry, these materials are promising to realize a high giant magnetoresistance at room temperature.     

ITER屏蔽包层第一壁人工缺陷模块热传导计算与分析

设计了3个外形一致的模块,其中两个在铍铜界面处预制有不同尺寸、形状和位置的缺陷,另一个是无缺陷的完整模块。通过有限元计算方法,分析了预制缺陷对温度分布的影响。通过无缺陷的完整模块的传热分析,评估有效的缺陷位置区域,计算了不同尺寸、形状、位置的缺陷的温度分布;根据对热传导基本公式中的各个量分别进行研究,并通过比较各种因素,得到了缺陷影响铍和铜合金界面温度的主要因素。     

A new stable polycrystalline Be2C monolayer: A direct semiconductor with hexa-coordinate carbons

In this paper, by means of the first principles calculations based on density functional theory, a new polycrystalline two-dimensional Be₂C namely Be₂C-III monolayer with orthorhombic atomic configuration is predicted. In this proposed monolayer, Be and C atoms are buckled in four different planes, in which each carbon atom binds to six beryllium atoms, while each beryllium atom is shared by three carbon and its three neighboring beryllium in a quasi-planar structure. First principles calculations confirmed that the new Be₂C-III monolayer is energetically, kinetically, and thermally stable. Through electronic properties investigations, it is found that the proposed monolayer is a direct semiconductor with a medium band gap of 1.75 (2.54 eV) calculated by PBE (HSE06) level of theory which can be effectively modulated by biaxial external strains. As a direct band gap semiconductor with high stabilities this new Be₂C monolayer is a promising candidate for application in electronics and optoelectronics devices.     

A complete set of integrals and solutions to the Szekeres system

The Szekeres system is an ODE system arising from the Szekeres cosmological model. The paper presents the way to solve it using its four global independent first integrals. It also contains the complete set of its solutions in the particular cases, related to the set where the integrals are indefinite.     

高压下YB6的电子结构与光学性质的第一性原理研究

本文从第一性原理出发,基于密度泛函理论体系下的广义梯度近似（GGA）方法,对不同压力下YB6的电子结构及光学性质方面进行了研究。结果表明：在一定的压力范围内随着压力的增大,费米面以上的能带往高能量处移动,费米面以下的能带往低能量处移动。能量损失谱的第一个峰随着压力的增大往高能量处移动,并且峰强增大。这表明可以通过压力来调节YB6在可见光区的吸收谷的位置及强度,在高压下YB6将展现更好的隔热性能。     

锗烯在金属衬底上的结构及电子性质的第一性原理研究

基于密度泛函理论的第一性原理计算,我们系统的研究了锗烯在Pt(111)、Au(111)和Al(111)表面的几何和电子结构.在这三种金属衬底上寻找到了9种结构,其中Al(111)-a、Au(111)-b和Pt(111)-c结构就是目前实验上已经成功制备的结构.我们还发现了其余6种目前理论和实验均没有提出,此外,Al(111)-b、Au(111)-a和Pt(111)-b结构的Dirac态仍保留,这些结构的形成能均大于范德瓦尔斯作用,因此非常有希望在实验上制备出来,应用于量子自旋霍尔效应的研究.本文的研究为锗烯在半导体衬底上的制备及应用奠定了理论基础.     

团簇ConAgm (n +m =13)表面吸附C2H4的第一性原理研究

基于密度泛函理论的第一性原理计算方法,本文对ConAgm(n+m=13)团簇的几何结构进行优化后,研究了C2H4分子在这类团簇的表面吸附行为,讨论了团簇的平均结合能、二阶能量差分、稳定性、DOS以及吸附前后键长的变化情况。结果表明,C2H4在团簇top位的吸附主要为物理吸附,而在face位和bridge位的吸附主要为化学吸附。吸附后,C2H4@Ag13的稳定性高于C2H4@Co13,且在face位吸附时C2H4@Co2Ag11的结构最为稳定。随着Co原子数的增加,团簇中原子间成键能力减弱,而d电子轨道则呈现出较强的相互作用,并导致其向能量相对高处发生转移     

空间型中紧致无边子流形上的第一特征值

得到了两个关于空间形式中紧致无边子流形的广义位置向量场和其上Laplace算子第一特征值λ_1的积分不等式。并由此首先给出了λ_1与其上界间的间隔估计,其次得到了此紧致无边子流形等距浸入在空间形式的测地超球面或等距于测地超球面的充分条件,推广了Deshmukh[6]在欧氏空间中的相应结论。     

A Modified Analytic Function Space Feynman Integral of Functionals on Function Space

In this paper, the authors introduce a class of functionals. This class forms a Banach algebra for the special cases. The main purpose of this paper is to investigate some properties of the modified analytic function space Feynman integral of functionals in the class. Those properties contain various results and formulas which were not obtained in previous papers. Also, the authors establish some relationships involving the first variation via the translation theorem on function space. In partic...