Variational principles for two kinds of extended Korteweg—de Vries equations

Variational principles are constructed using the semi-inverse method for two kinds of extended Korteweg—de Vries (KdV) equations, which can be regarded as simple models of the nonlinear oceanic internal waves and atmospheric long waves, respectively. The obtained variational principles have also been proved to be correct.     

双轴应变条件下单层MoSe2电子结构和拉曼光谱的第一性原理计算

二硒化钼的层间相互作用强,单层结构具有更低的带隙和更好的稳定性.由于独特的光学性质和优异的电学性能受到研究人员的广泛关注.本文基于密度泛函理论的第一原理,计算和分析了在双轴拉伸压缩应变条件下单层MoSe₂能带结构,拉曼光谱和声子谱的变化规律以及性质产生的原因.在拉伸压缩应变作用下,直接带隙转变为间接带隙.当拉伸应变达到12%时,材料发生半导体-金属相变.当压缩应变达到6%时,声子谱中开始出现虚频率,表明结构开始变得不稳定.     

Gap states at organic-metal interfaces: A combined spectroscopic and theoretical study

A systematic understanding and controlling of gap states formed at the organic-metal interfaces is a key factor for fabricating functional organic-metal systems, as in case of heterojunctions in semiconductor devices. We report here the characterization of gap states near the Fermi level of metal substrate by metastable atom electron spectroscopy and first-principles density functional calculations. The gap states in organic-metal systems are classified into two types, i.e., chemisorption-induced gap states (CIGSs) and complex-based gap states (CBGSs). CIGSs can be further classified whether the metal wave function tails a short distance into the chemisorbed species with the exponential decay (damping type) or is exposed sufficiently to the chemisorbed species by mixing with the organic orbitals (propagating type). CIGSs observed in alkanethiolate and C₆₀ on Pt(1 1 1) are their typical examples, respectively. As a consequence, alkanethiolate serves as a poor mediator of metal wave function, whereas C₆₀ acts as a good mediator, which is responsible for tunneling mechanism and eventually electric conductivity in the relevant metal-organic-metal junctions. CBGSs are identified in bathocuproine films deposited on K-covered Au, where the K atoms migrate into the film to form an organic-metal complex. The CBGSs are distributed over the multilayer film, in contrast to the case of CIGS. With increasing film thickness, the CBGSs exhibit incommensurate energy shifts with the valence band top of the film, indicating that the Schottky-Mott model breaks down as evaluating charge transport in organic-metal systems.     

H2S在Fe(100)面吸附的第一性原理研究

基于密度泛函理论第一性原理, 在广义梯度近似下, 研究了表面覆盖度为0.25 ML (monolayer)时硫化氢分子在Fe(100)面吸附的结构和电子性质, 并与单个硫原子吸附结果进行了对比. 结果表明: 硫化氢分子吸附在B2位吸附能最小为-1.23 eV, 最稳定, B1位吸附能最大为-0.01 eV, 最不稳定; 并对硫化氢分子在B1位和B2位吸附后的电子态密度进行了分析, 也表明了吸附在B2位稳定, 且吸附在B2位后硫化氢分子几何结构变化不大; 将硫化氢中硫原子吸附与单个硫原子吸附的电子性质进行了比较, 发现前者吸附作用非常微弱; 同时对吸附后的Fe(100)面进行了对比, 单个硫原子吸附的Fe(100)面电子态密度出现了一系列峰值且离散分布, 生成了硫化亚铁, 表明在硫化氢环境下, 主要是硫化氢析出的硫原子发生了吸附. 关键词： 第一性原理 Fe(100)表面 吸附能 硫化氢     

基于第一性原理的锂空气电池钌掺杂石墨烯正极 氧还原反应机理研究

双电解液锂空气电池因其高理论能量密度受到广泛研究,但电池正极侧氧还原反应(ORR)速率低,其反应速率是限制锂空气电池发展的主要因素之一.本文提出了以钌(Ru)掺杂单层石墨烯作为正极ORR催化剂,采用第一性原理计算nRu (n=1～3)掺杂石墨烯的电子结构和氧气在Ru掺杂石墨烯表面的吸附性能,并以过渡态搜索方法获得ORR反应路径,研究碱性溶液中Ru掺杂单层石墨烯作用下的ORR机理.研究结果表明,经Ru原子掺杂后,石墨烯能够获得稳定的掺杂结构,且电导率显著提升.同原始单层石墨烯相比,Ru掺杂石墨烯增强了对O₂的吸附能力.在三Ru(n=3)掺杂石墨烯表面进行的ORR无需克服任何能垒.此外,三Ru掺杂石墨烯表面对OH基团的吸附能最低,有利于ORR的连续进行.研究表明三Ru掺杂石墨烯有望成为一种新型的ORR催化剂以提高双电解液锂空气电池的性能.     

Mo掺杂4H-SiC的磁性和光学性能的第一性原理研究

基于第一性原理密度泛函理论（DFT）的广义梯度近似（GGA）的平面波赝势法（PBE）,计算了4H-SiC的本征体系、过渡金属元素Mo单掺杂4H-SiC体系的电子结构、磁性和光学特性。结果表明：Mo掺杂将导致4H-SiC由本征非磁性变为p型磁性半导体材料,其带隙值由2.88 eV 变为0.55 eV。当Mo掺杂浓度为1.359×1021 cm-3时,磁矩为0.98 ,这表明掺Mo后的4H-SiC材料可以作为自旋电子元器件的备选材料。此外,Mo掺杂4H-SiC体系在（100）和（001）方向的静态介电常数分别为3.780和3.969。介质函数虚部不为0的起始点发生红移,表明掺杂使电子更容易跃迁。     

An Interacting Gauge Field Theoretic Model for Hodge Theory: Basic Canonical Brackets

We derive the basic canonical brackets amongst the creation and annihilation operators for a two （1 ＋ 1）- dimensional （2D） gauge field theoretic model of an interacting Hodge theory where a U（1） gauge field （Aμ） is coupled with the fermionic Dirac fields （ψ and ψ）. In this derivation, we exploit the spin-statistics theorem, normal ordering and the strength of the underlying six infinitesimal continuous symmetries （and the concept of their generators） that are present in the theory. We do not use the definition of the canonical conjugate momenta （corresponding to the basic fields of the theory） anywhere in our whole discussion. Thus, we conjecture that our present approach provides an alternative to the canonical method of quantization for a class of gauge field theories that are physical examples of Hodge theory where the continuous symmetries （and corresponding generators） provide the physical realizations of the de Rham cohomological operators of differential geometry at the algebraic level.     

化工原理问题导向式线上教学的探索与实践*

以化学制药专科专业化工原理课程为例,阐述问题导向式线上教学的课程设计思路及框架,探索由被动教到主动学的线上教学途径。通过对“流体流动与输送单元”的教学设计,从课前、课中和课后论述了以“问题”为中心的线上教学过程和实施情况,并说明了线上授课的教学效果。     

First-principle study on the effect of high Li-2N co-doping on the conductivity of ZnO

Based on the density functional theory (DFT), using first-principles plane-wave ultrasoft pseudopotential method, the models of the unit cell of pure ZnO and two highly Li-2N co-doped supercells of Zn_0.9375Li_0.0625O_0.875N_0.125 and Zn_0.9167Li_0.0833O_0.8333N_0.1667 were constructed, and the geometry optimization for the three models was carried out. The total density of states (TDOS) and the band structures (BS) were also calculated. The calculation results showed that in the range of high doping concentration, when the co-doping concentration is more than a certain value, the conductivity decreased with the increase of co-doping concentration of Li-2N in ZnO, which agrees with the change trend of the experimental results.