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.     

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     

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.     

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。     

Insights into interfacial stability of Li6PS5Cl solid electrolytes with buffer layers

The large interfacial resistance seriously restricts the development of all-solid-state lithium batteries (ASSLBs). In our work, first-principles calculations are employed to investigate the interfacial properties on lithium (Li) metal anode/Li₆PS₅Cl solid electrolyte (LPSCl) interface system as well as buffer layers (Li₂S) effects. The stable interface structures, Li/LPSCl, L₂S/LPSCl and Li/L₂S, are established at atomic level. We find that PS₄ tetrahedral structure has been seriously destroyed in Li/LPSCl interface, whereas the presence of Li₂S buffer layers may smooth the interface without PS₄ tetrahedral damage occurred. In addition, the electronic structure of interface indicates that solid electrolyte interphases are not easy to form on LPSCl surfaces considering buffer layers effects, which may improve the stability of anode/solid electrode interface. Moreover, the calculated energies of exchange ions between Li metal and solid electrolyte with buffer layers suggest that the Li₂S interposition can suppress the atoms diffusion in LPSCl layers, and provide a smooth interface structure, which may promote the stability of Li/LPSCl interface. This work on the atomic scale will offer a useful perspective for designing high performance of solid electrolytes to enhance good cyclability in ASSLBs.     

A study on monolayer MoS2 doping at the S site via the first principle calculations

Through the first principle calculation, electronic properties of monolayer MoS₂ doped with single, double, triple and tetra-atoms of P, Cl, O, Se at the surface S site are discussed. Among the substitutional dopant, our calculation results show that when P atoms are doped on a monolayer MoS₂, a shift in the Fermi energy into the valence band is observed, making the system p-type. Meanwhile, band gap gradually decreases as increasing the number of P atoms. On the contrary, Cl is identified as a suitable n-type dopant. It is observed that Cl for initial three dopant behaved as magnetic and afterwards returned to non-magnetic behavior. The band gap of the Cl doped system is also dwindling gradually. Finally, O and Se doped systems have little effect on electronic properties near band gap. Such doping method at the S site, and the TDOS and PDOSs of each doping system provide a detailed of understanding toward working mechanism of the doped and the intrinsic semiconductors. This doping model opens up an avenue for further clarification in the doping systems as well as other dopant using this method.     

New exact solutions of Burgers’ type equations with conformable derivative

In this paper, the new exact solutions for some nonlinear partial differential equations are obtained within the newly established conformable derivative. We use the first integral method to establish the exact solutions for time-fractional Burgers’ equation, modified Burgers’ equation, and Burgers–Korteweg–de Vries equation. We report that this method is efficient and it can be successfully used to obtain new analytical solutions of nonlinear FDEs.     

B、N单掺杂3C-SiC电子结构和光学性质的第一性原理研究

采用第一性原理的密度泛函理论赝势平面波方法,计算了未掺杂与B、N单掺杂3C-SiC的电子结构和光学性质.结果表明:掺杂改变了3C-SiC费米面附近的电子结构;B掺杂使得禁带宽度减小,价带顶上移,费米能级进入价带,形成p型半导体;N掺杂使得禁带宽度减小,导带底下移,费米能级进入导带,形成n型半导体.B、N掺杂均提高了3C-SiC在低能区的折射率、消光系数和吸收系数,增强了对红外光谱的吸收.     

Hole doped α-MgAgSb as potential low temperature thermoelectric materials

The electronic structures and thermoelectric transport properties of α-MgAgSb were systematically investigated by using the first principles calculations combined with the Boltzmann transport equations. It is found that the thermoelectric properties of p-type α-MgAgSb are much better than those of n-type one, which originates from the steeper slope of the density of states at the edge of the valence band. By analyzing the density of states and partial charge density, we conclude that p-doping at the Mg-site does not modify the electronic states, but can optimize the carrier concentration. The effects of the carrier concentration and temperature on the thermoelectric transport properties of p-type α-MgAgSb are discussed in detail and the calculated results show good agreement with the experimental values. The p-type α-MgAgSb exhibit high thermoelectric performance and is a promising candidate for the low-temperature thermoelectric applications     

CH_4、H_2O在CaCO_3(010)表面吸附的第一性原理研究

基于密度泛函理论第一性原理方法,研究了CH_4和H_2O在CaCO_3(010)面上各高对称位的吸附情况,优化了CH_4与H_2O在T位、 B位和H位的吸附模型结构,计算了其在各高对称位的吸附能,并对其各自最稳定的吸附位吸附前后的物理结构和电子态密度进行了对比分析.结果表明:CH_4、 H_2O分子分别在LBⅢ位、 SBⅢ位最稳定,吸附能分别为-0.405 eV、-0.138 eV,是一种物理吸附,吸附前后键长键角的变化较小,表现为亲气;吸附后CH_4和H_2O的态密度曲线整体向低能量区偏移约7.5 eV、 5eV,吸附后CH_4和H_2O结构都更加稳定,吸附作用对CH_4和H_2O分子的电子结构影响显著.