高斯光束斜入射法布里-珀罗干涉腔后的反射光强分布

基于多光束干涉原理,推导了高斯光束斜入射法布里-珀罗干涉仪后的反射光强表达式.在此基础之上数值研究了入射角对高斯光束的反射特性的影响.研究结果表明:当法布里-珀罗干涉腔的腔长满足反共振时,随着入射角的增大,反射光的光强分散,峰值强度下降后呈现出幅度衰减的波动;峰值位置随着入射角的增大,呈现出幅度越来越小的振荡偏移;光斑大小随入射角的增大,呈现出幅度减小的振荡.     

Cr和W掺杂的单层MoS2电子结构的第一性原理研究

采用密度泛函理论框架下的第一性原理平面波赝势方法, 研究了Cr和W掺杂对单层二硫化钼(MoS₂)晶体的电子结构性质的影响. 计算结果表明: 当掺杂浓度较高时, W对MoS₂的能带结构几乎没有影响, 而Cr的掺杂则影响很大, 表现为能带由直接带隙变为间接带隙, 且禁带宽度减小. 通过进一步分析, 得出应力的产生是导致Cr掺杂的MoS₂电子结构变化的最直接的原因.     

First principle study of LiXS_2(X=Ga,In) as cathode materials for Li ion batteries

From first principle calculations, we demonstrate that LiXS_2(X = Ga, In) compounds have potential applications as cathode materials for Li ion batteries. It is shown that Li can be extracted from the LiXS_2 lattice with relatively small volume change and the XS_4 tetrahedron structure framework remains stable upon delithiation. The theoretical capacity and average intercalation potential of the LiGaS_2(LiInS_2) cathode are 190.4(144._2) m Ah/g and 3.50 V(3.53 V). The electronic structures of the LiXS_2 are insulating with band gaps of _2.88 eV and 1.99 eV for X = Ga and In, respectively.However, Li vacancies, which are formed through delithiation, change the electronic structure substantially from insulating to metallic structure, indicating that the electrical conductivities of the LiXS_2 compounds should be good during cycling.Li ion migration energy barriers are also calculated, and the results show that Li ion diffusions in the LiXS_2 compounds can be as good as those in the currently widely used electrode materials.     

应力对硅烯上锂吸附的影响

本文采用基于密度泛函理论的第一性原理平面波赝势方法研究了双轴应力作用下锂原子吸附硅烯的结构及其稳定性. 计算结果表明,在拉应力和一定的压应力作用下,锂吸附的硅烯体系基本保持原有的结构. 而当更大的压应力作用时,硅烯产生了向锂原子方向凸起的结构变化,所得到的体系的总能也有明显地下降. 本文通过对各种应力下的硅烯声子谱的计算,分析了在压应力作用下锂吸附的硅烯结构不稳定的原因. 关键词： 硅烯 应力 第一性原理 声子谱     

Configurational entropy-induced phase transition in spinel LiMn2O4

The spinel-type LiMn$_{2}$O$_{4}$ is a promising candidate as cathode material for rechargeable Li-ion batteries due to its good thermal stability and safety. Experimentally, it is observed that in this compound there occur the structural phase transitions from cubic ($Fd\bar{3}m)$ to tetragonal ($I4_{1}/{amd}$) phase at slightly below room temperature. To understand the phase transition mechanism, we compare the Gibbs free energy between cubic phase and tetragonal phase by including the configurational entropy. Our results show that the configurational entropy contributes substantially to the stability of the cubic phase at room temperature due to the disordered Mn$^{3+}$/Mn$^{4+}$ distribution as well as the orientation of the Jahn-Teller elongation of the Mn$^{3+}$O$_{6}$ octahedron in the the spinel phase. Meanwhile, the phase transition temperature is predicted to be 267.8 K, which is comparable to the experimentally observed temperature. These results serve as a good complement to the experimental study, and are beneficial to the improving of the electrochemical performance of LiMn$_{2}$O$_{4}$ cathode.     

Physics of electron and lithium-ion transport in electrode materials for Li-ion batteries

The physics of ionic and electrical conduction at electrode materials of lithium-ion batteries(LIBs) are briefly summarized here, besides, we review the current research on ionic and electrical conduction in electrode material incorporating experimental and simulation studies. Commercial LIBs have been widely used in portable electronic devices and are now developed for large-scale applications in hybrid electric vehicles(HEV) and stationary distributed power stations. However,due to the physical limits of the materials, the overall performance of today's LIBs does not meet all the requirements for future applications, and the transport problem has been one of the main barriers to further improvement. The electron and Li-ion transport behaviors are important in determining the rate capacity of LIBs.     

应变对单层二硫化钼能带影响的第一性原理研究

采用密度泛函理论框架下的第一性原理平面波赝势方法,研究了双轴拉应变下单层二硫化钼晶体的电子结构性质．本文的计算结果表明对单层二硫化钼晶体施加一个很小的应变（0．5％）时,其能带结构由直接带隙转变为间接带隙．随着应变的增加,能带仍然保持间接带隙的特征,且禁带宽度呈现线性下降的趋势．通过对单层二硫化钼晶体态密度和投影电荷密度的进一步分析,揭示了单层二硫化钼晶体能带变化的原因．     

氢空位簇调控锗烷的电子结构和分子掺杂

锗烷因其合适的带隙、较高的电子迁移速率、较好的环境稳定性、较小的电噪声和超薄的几何结构,有望取代现有硅基或锗基材料成为下一代半导体器件的理想载体.基于密度泛函理论和非平衡格林函数的第一性原理方法,研究了不同构型和浓度的氢空位簇对锗烷电子结构及锗烷中四硫富瓦烯(tetrathiafulvalene,TTF)分子掺杂性能的影响.计算结果表明,不同构型氢空位簇的引入可诱导Germanane Dehydrogenated-x H (G_D–xH)体系产生不同性质的磁性,且磁矩大小亦与Lieb定理的预测结果相符,并能在GD-x H (x=1, 4, 6)体系自旋向下的能带结构中实现由缺陷态引起的类p型半导体掺杂效应,其电子激发所需的能量则会随着体系脱氢浓度的升高而不断降低.吸附TTF分子后, G/TTF和G_D-xH/TTF (x=1, 2, 6)体系表现出分子掺杂效应,且GD-x H/TTF (x=1, 6)体系因分子轨道与缺陷态的杂化作用,可在自旋向上与自旋向下的能带结构中形成不同的掺杂类型.进一步的量子输运计算还表明, Armchair和Zigzag...     

Phase-sensitive nonclassical properties of photon-added-then-subtracted coherent squeezed states

We investigate the nonclassical properties of the photon-added-then-subtracted coherent squeezed state(PASCSS) via the sub-Poissonian statistics,the photon-number distribution,and the negativity of the Wigner function.It is found that the PASSCS is a superposition state of D(β)S(ζ)|0>,D(β)S(ζ)|1>,and D(β)S(ζ)|2>.We find that the Mandel Q parameter,the photon-number distribution,and the negative volume of the Wigner function of the PASCSS are all periodic functions of the compound φ-θ/2 with a period π involved with squeezing and displacement parameters.     

Comparisons between adsorption and diffusion of alkali,alkaline earth metal atoms on silicene and those on silicane:Insight from first-principles calculations

The adsorption and diffusion behaviors of alkali and alkaline-earth metal atoms on silicane and silicene are both investigated by using a first-principles method within the frame of density functional theory.Silicane is staler against the metal adatoms than silicene.Hydrogenation makes the adsorption energies of various metal atoms considered in our calculations on silicane significantly lower than those on silicene.Similar diffusion energy barriers of alkali metal atoms on silicane and silicene could be observed.However,the diffusion energy barriers of alkali-earth metal atoms on silicane are essentially lower than those on silicene due to the small structural distortion and weak interaction between metal atoms and silicane substrate.Combining the adsorption energy with the diffusion energy barriers,it is found that the clustering would occur when depositing metal atoms on perfect hydrogenated silicene with relative high coverage.In order to avoid forming a metal cluster,we need to remove the hydrogen atoms from the silicane substrate to achieve the defective silicane.Our results are helpful for understanding the interaction between metal atoms and silicene-based two-dimensional materials.