排序方式: 共有10条查询结果,搜索用时 25 毫秒
1
1.
2.
An application of the coupled-channels optical method is given for the energy-dependent phenomena of positron-hydrogen resonances below the n=2 excitation threshold. The equivalent local optical potential is used to account for the target polarization and positronium formation. The calculation includes 9 explicitly physical coupled channels. The lowest S-wave resonance energy position and new resonances are found. Angular dependence of the cross section in the resonance region are investigated. 相似文献
3.
Structure prediction,electronic, and mechanical properties of alkali metal MB_(12)(=Be,Mg, Ca,Sr) from first principles
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Using the particle swarm optimization algorithm on structural search methods, we focus our crystal structures search on boron-rich alkali metal compounds of MB12(M = Be, Mg, Ca, Sr) with simulation cell sizes of 1–2 formula units(f.u.)at 0 GPa. The structure, electronic, and mechanical properties of MB12 are obtained from the density functional theory using the plane-wave pseudopotential method within the generalized gradient approximations. The formation enthalpies of MB12 regarding to solid metal M and solid alpha-boron suggested the predicted structures can be synthesized except for BeB12. The calculated band structures show MB12(M = Be, Mg, Ca, Sr) are all indirect semiconductors. All the calculated elastic constants of MB12 satisfy the the mechanical stable conditions. The mechanical parameters(i.e., bulk modulus,shear modulus, and Young’s modulus) are derived using the Voigt–Reuss–Hill method. The G/B ratios indicated that the MB12 should exhibit brittle behavior. In addition, the hardness, Debye temperature, universal anisotropic index, and the percentage of anisotropy in compression and shear are also discussed in detail. We hope our results can inspire further experimental study on these boron-rich alkali-metal compounds. 相似文献
4.
Investigations of resonances and threshold behaviors in positron-helium scattering have been made using the momentum-space coupled-channels optical method.The positronium formation channels are considered via an equivalent-local complex potential.The s-wave resonances and the Wigner cusp feature at the positronium(n = 1) formation threshold are compared with the previous reports.The p-and the d-wave resonances and a Wigner cusp feature at the positronium(n = 2) formation threshold are reported for the first time. 相似文献
5.
The low energy scattering of electrons by sodium at incident energies up to ionization threshold are calculated by applying the momentum space coupled-channel-optical (CCO) method. The present results are in good agreement with the previous experimental and theoretical results. Furthermore, three resonances in the total cross sections observed by previous experiments are proved by the present calculation. 相似文献
6.
The direct ionization cross sections for electron scattering by nitrogen are calculated by applying an equivalentlocal optical model from 15eV to 1100eV. The present results are compared with the experimental data and other theoretical calculation results. 相似文献
7.
An application of the coupled-channels optical method is given for the energy-dependent phenomena of positron-hydrogen resonances below the n=2 excitation threshold.The equivalent local optical potential is used to account for the target polarization and positronium formation.The calculation includes 9 explicitly physical coupled channels.The lowest S-wave resonance energy position and new resonances are found.Angular dependence of the cross section in the resonance region are investigated. 相似文献
8.
An approximation formula is developed to determine the tune-out wavelengths for the ground states of the alkalinemetal atoms lithium,sodium and cesium from the existing relativistic reduced matrix elements and experimental energies.The first longest tune-out wavelengths for Li,Na,and Cs are 670.971 nm,589.557 nm,and 880.237 nm,respectively.This is in good agreement with the previous high precise results of 670.971626 nm,589.5565 nm,and 880.25 nm from the relativistic all-order many-body perturbation theory(RMBPT) calculation[Phys.Rev.A 84 043401(2011)]. 相似文献
9.
采用基于粒子群优化算法的结构预测程序CALYPSO, 并结合第一性原理的VASP程序, 在175 GPa发现NbSi2的奇异立方高压相. 在此结构中, Nb原子形成金刚石结构, 而Si原子则形成正四面体镶嵌在金刚石结构中. 声子谱计算结果表明该结构是动力学稳定的. 电子结构分析表明, 六角相和立方相NbSi2均为金属, 对金属性贡献较大的是Nb原子, 而且Nb和Si原子之间存在明显的p-d杂化现象, 电荷更多地聚集在Si四面体中. 利用“应力应变”方法, 计算了NbSi2的弹性常数, 分析了其体积模量、剪切模量、杨氏模量和德拜温度等热动力学性质随压力的变化并进行了详细的讨论. 根据剪切模量和体积模量的比值分析了NbSi2两种相结构的脆性和延展性, 发现压力会导致六角相NbSi2的延展性增加, 但对立方相结构的延展性影响较小; 采用经验算法计算了NbSi2两种相结构硬度变化情况, 结合这一比值进行了详细的分析. 弹性各向异性计算结果表明, 随着压力增加, 六角结构的各向异性增强, 而立方结构的各向异性减小. 相似文献
10.
利用Ag/tris-(8-hydroxyquinoline) aluminum(Alq3)/Ag/Alq3/Ag这一金属/有机半导体多层结构作为阳极,实现了超低效率滚降的顶发射白光器件。在该器件中,我们在蓝光和橙光发光单元之间引入一个薄的4,4′-bis(9-carbazolyl)-2,2′-biphenyl(CBP)层,从而减少橙光发光层与蓝光发光层的Dexter能量传递,用以改善白光器件发光光谱及效率。通过优化微腔设计,实现了对橙光磷光材料发射的调控。最终,我们获得了在60 000 cd/m2亮度下效率滚降仅为17%的顶发射白光器件。在效率方面,虽然顶发射白光器件与底发射白光器件不相上下,但由于微腔效应的存在,顶发射白光器件的效率滚降却远低于底发射白光器件的效率滚降。 相似文献
1