High-throughput identification of one-dimensional atomic wires and first principles calculations of their electronic states

Low dimensional materials are suitable candidates applying in next-generation high-performance electronic, optoelectronic, and energy storage devices because of their uniquely physical and chemical properties. In particular, onedimensional(1 D) atomic wires(AWs) exfoliating from 1 D van der Waals(vd W) bulks are more promising in next generation nanometer(nm) even sub-nm device applications owing to their width of few-atoms scale and free dandling bonds states. Although several 1 D AWs have been experimentally prepared, few 1 D AW candidates could be practically applied in devices owing to lack of enough suitable 1 D AWs. Herein, 367 kinds of 1 D AWs have been screened and the corresponding computational database including structures, electronic structures, magnetic states, and stabilities of these 1 D AWs has been organized and established. Among these systems, unary and binary 1 D AWs with relatively small exfoliation energy are thermodynamically stable and theoretically feasible to be exfoliated. More significantly, rich quantum states emerge,such as 1 D semiconductors, 1 D metals, 1 D semimetals, and 1 D magnetism. This database will offer an ideal platform to further explore exotic quantum states and exploit practical device applications using 1 D materials. The database are openly available at http://www.dx.doi.org/10.11922/sciencedb.j00113.00004.     

Density functional theory investigation on lattice dynamics,elastic properties and origin of vanished magnetism in Heusler compounds CoMnVZ (Z= Al,Ga)

The lattice dynamics, elastic properties and the origin of vanished magnetism in equiatomic quaternary Heusler compounds CoMnVZ (Z=Al, Ga) are investigated by first principle calculations in this work. Due to the similar constituent atoms in CoMnVAl and CoMnVGa compounds, they are both stable in LiMgPdSn-type structure with comparable lattice size, phonon dispersions and electronic structures. Comparatively, we find that CoMnVAl is more structurally stable than CoMnVGa. Meanwhile, the increased covalent bonding component in CoMnVAl enhances its mechanical strength and Vickers hardness, which leads to better comprehensive mechanical properties than those of CoMnVGa. Practically and importantly, structural and chemical compatibilities at the interface make non-magnetic semiconductor CoMnVAl and magnetic topological semimetals Co₂MnAl/Ga more suitable to be grown in heterostructures. Owing to atomic preferential occupation in CoMnVAl/Ga, the localized atoms Mn occupy C (0.5, 0.5, 0.5) Wyckoff site rather than B (0.25, 0.25, 0.25) and D (0.75, 0.75, 0.75) Wyckoff sites in LiMgPdSn-type structure, which results in symmetric band filling and consequently drives them to be non-magnetic. Correspondingly, by tuning localized atoms Mn to occupy B (0.25, 0.25, 0.25) or/and D (0.75, 0.75, 0.75) Wyckoff sites in off-stoichiometric Co-Mn-V-Al/Ga compounds and keeping the total valence electrons as 24, newly compensated ferrimagnetic compounds are theoretically achieved. We hope that our work will provide more choices for spintronic applications.     

镁离子电池正极材料VS_4掺杂改性的第一性原理研究

阳离子掺杂能够有效提高材料的电化学性能,而对掺杂材料结构和电化学性质的研究能从理论上解释产生这种变化的原因.本文采用基于密度泛函理论的第一性原理方法,研究了过渡族金属掺杂的镁离子电池正极材料TM_(0.125)V_(0.875)S_4(TM=Mo、Fe、Co、Ni)的几何和电子结构变化,计算结果显示:通过采用范德华力修正的GGA+vdw-DF方法,获得了和实验结果相一致的晶格常数.阳离子掺杂后,a轴和b轴晶格常数减小,而c轴晶格常数增大.电子态密度分析表明离子掺杂能够有效降低带隙,提高材料的电子电导率.通过对镁离子扩散进行微动弹性带(NEB)计算,发现Fe掺杂能够有效降低扩散能垒,提高材料的离子迁移率.     

稀土元素La掺杂对AlN性能影响的第一性原理研究

本文通过基于密度泛函理论的第一性原理计算方法研究了稀土元素La掺杂对纤锌矿结构AlN力学性能及压电性能的影响.计算得到的AlN各项力学性能及压电性能与实验值较吻合.掺杂稀土元素La会降低其体模量、剪切模量与杨氏模量,但会使AlN由脆性材料转变为韧性材料.压电性能计算结果表明,掺杂稀土元素La后,可使体系的压电性能提升15%左右.电子结构分析结果表明La的引入会降低体系中化学键的作用强度,从而提升了体系的塑性及压电性能.     

Moderate deviations for marked Hawkes processes

We consider a linear Hawkes process with random marks. Some limit theorems have been studied by Karabash and Zhu [Stoch. Models, 31, 433–451 (2015)]. In this paper, we obtain a moderate deviation principle for marked Hawkes processes.     

On a free boundary problem for a class of anisotropic equations

This paper deals with a certain condenser capacity in an anisotropic environment. More precisely, we are going to investigate a free boundary problem for a class of anisotropic equations on a ring domain N≥2. Our aim is to show that if the problem admits a solution in a suitable weak sense, then the underlying domain Ω is a Wulff‐shaped ring. The proof makes use of a maximum principle for an appropriate P‐function, in the sense of L. E. Payne, a Rellich type identity and some geometric arguments involving the anisotropic mean curvature of the free boundary. Copyright © 2016 John Wiley & Sons, Ltd.     

生物工程专业化工原理理论教学的改革与探索

在当前高等学校注重创新创业人才培养的教育改革背景下,从生物工程专业化工原理理论教学如何从教学内容的载体、教学方法、考核方式等方面改革出发,探讨了适合工科院校化工原理教学加强实践和创新能力,培养创新型人才的新途径。     

基于“雨课堂+对分易”的化工原理混合教学模式探索与实践*

根据新工科建设要求,应积极探索符合时代特征和工程教育规律的培养模式。针对化工原理课程特点,引入“雨课堂”和“对分易”2种现代网络教学平台作为混合式教学工具。雨课堂实现了课前-课中-课后的三环节教学模式;对分易通过提交章节思维导图及“亮考帮”作业,结合课堂讨论,逐一击破学生学习难点,多方位激发学生自主学习的积极性,增加了课堂互动性,提高了教学质量。     

Frictional passage of fluid through inhomogeneous porous system: a variational principle

A Fermat-like principle of minimum time is formulated for nonlinear steady paths of fluid flow in inhomogeneous isotropic porous media where fluid streamlines are curved by a location dependent hydraulic conductivity. The principle describes an optimal nature of nonlinear paths in steady Darcy’s flows of fluids. An expression for the total path resistance leads to a basic analytical formula for an optimal shape of a steady trajectory. In the physical space an optimal curved path ensures the maximum flux or shortest transition time of the fluid through the porous medium. A sort of “law of bending” holds for the frictional fluid flux in Lagrange coordinates. This law shows that—by minimizing the total resistance—a ray spanned between two given points takes the shape assuring that a relatively large part of it resides in the region of lower flow resistance (a ‘rarer’ region of the medium).     

Cage‐Like B41+ and B422+: New Chiral Members of the Borospherene Family

The newly discovered borospherenes B₄₀^?/0 and B₃₉^? mark the onset of a new class of boron nanostructures. Based on extensive first‐principles calculations, we introduce herein two new chiral members to the borospherene family: the cage‐like C₁ B₄₁⁺ ( 1 ) and C₂ B₄₂²⁺ ( 2 ), both of which are the global minima of the systems with degenerate enantiomers. These chiral borospherene cations are composed of twelve interwoven boron double chains with six hexagonal and heptagonal faces and may be viewed as the cuborenes analogous to cubane (C₈H₈). Chemical bonding analyses show that there exists a three‐center two‐electron σ bond on each B₃ triangle and twelve multicenter two‐electron π bonds over the σ skeleton. Molecular dynamics simulations indicate that C₁ B₄₁⁺ ( 1 ) fluctuates above 300 K, whereas C₂ B₄₂²⁺ ( 2 ) remains dynamically stable. The infrared and Raman spectra of these borospherene cations are predicted to facilitate their experimental characterizations.