Schottky Barrier Formation at a Carbon Nanotube-Scandium Junction

Recent experiment shows that scandium （Sc） can make a good performance contact with carbon nanotubes （CNTs） to fabricate n-type field effect transistor （n-FET）. We study the Schottky barrier （SB） of scandium （Sc） and palladium （Pd） with a （8,0） single-wall CNT （SWCNT） using first-principles calculation. It is found that the p-type SB height （SBH） of the Pd-CNT contact is about 0.34 eV, which is in good agreement with the experimental data. For the Sc-CNT contact, an n-type contact is formed and the SBH is about O.08eV in agreement with the experimental observations. Our calculation demonstrates that by contacting CNT with Pd and Sc, p-FET and n-FET can be fabricated, respectively. The dipole effect at the interface is used to explain our result.     

Li- Site and Metal-Site Ion Doping in Phosphate-Olivine LiCoPO4 by First-Principles Calculation

We present a first-principles investigation of the crystal and electronic structure as well as the average insertion voltage of the Li-site （by Na and Cr） and metal-site （by isovalent Ni, Zn, Ca, Mg and Mn and aliovalent Cu, Al, In, Mo and Zr） doped LiCoPO4. The results show that both the Li-site doping and metal-site doping may reduce the volume change of the material during Li extraction/reinsertion process. The metal doped at Li-site will block the path of Li ion diffusion. The doping by aliovalent transition metals will introduce defect levels in the energy band. It could influence the conductivity insertion voltage.     

The MAEAM Model and Anharmonic Theory for the Bulk Modulus of A1 Metal

The modified analytic embedded atom method （MAEAM） model and the anharmonic theory are used to study the bulk modulus of fcc A1 metal. The result shows that the bulk modulus can be described by a quadratic function of temperature. The result is in good agreement with the experimental data and theoretical results calculated by the first principle calculation etc. This outcome indicates that the temperature dependence of the bulk modulus for f cc A1 metal can be academically studied with the MAEAM model combining with the anharmonic theory.     

Bulk Modulus and Electronic Band Structure of ZnGa2Xa （X=S,Se）： a First-Principles Study

First-principles local density functional calculations are presented for the compounds ZnGa2X4 （X = S, Se）. We investigate the bulk moduli and electronic band structures in a defect chalcopyrite structure. The lattice constants and internal parameters are optimized. The electronic structures are analysed with the help of total and partial density of states. The relation between the cohesive energy and the unit cell volume is obtained by fully relaxed structures. We derive the bulk modulus of ZnGa2Xa by fitting the Birch-Murnaghan＇s equation of state. The extended Cohen＇s empirical formula agrees well with our ab initio results.     

Phase Transition and Thermodynamics of Ruthenium Diboride via First-Principles Calculations

The pressure induced phase transitions of RuB2 from the OsB2-type structure to the ReB2-type structure are investigated by first-principles calculations based on the plane-wave basis set with the generalized gradient ap- proximation for exchange and correlation. It is found that the phase transition occurs at 18.6 GPa. We predict the phase transition from the OsB2-type RuB2 to the ReB2-type RuB2 at high temperatures for the first time. The dependences of the heat capacity, thermal expansion coefficient, and the Grüneisen parameter on pressure and temperature for OsB2-type RuB2 and ReB2-type RuB2 are also investigated.     

时滞Duffing型微分方程周期解的存在唯一性

利用三角级数理论及压缩映射原理研究了时滞Duffing型方程ax″(t) bx(t) g(x(t-τ))=p(t),给出了此类Duffing型方程存在唯一周期解的几个充分条件.     

关于态叠加原理的认同与争议

给出了不同学者关于量子力学态叠加原理的几种表述,分析比较了关于该原理的有关观点的争议,并对其中的原因进行了讨论。     

激发态过程的多体理论方法

描述多电子体系的绝大部分参量可实验测量,如吸收光谱、发光光谱和激子效应等,都涉及电子激发态的正确描述。密度泛函理论(DFT)框架内的局域密度近似(LDA)作为第一性原理基态理论,即基于Kohn-Sham方程的解,是研究多粒子体系基态性质非常有力的工具。然而,体系激发态的第一性原理理论及其计算要比基态的理论计算复杂得多。关键问题在于描写基态和激发态时,粒子间的交换关联相互作用并不相同,而对于非均匀相互作用多粒子体系的交换关联能至今仍不清楚。不过,近年来关于激发态问题的研究,先后发展了许多描述电子激发态的理论,最重要的是基于准粒子概念和Green函数方程的多体微扰理论和含时间密度泛函理论(TDDFT)以及与此相关的描述电子-空穴相互作用的Bethe-Salpeter方程在凝聚态物理问题中的应用。其中最关键的物理量是粒子的自能算符Σ,它描述Hartree近似之外的交换和关联效应。虽然这些理论不可避免地也要引入某些近似,如对于Σ的一个好的近似就是Hedin的GW近似方法。对许多实际凝聚态体系的计算机模拟结果表明,GW近似是描述激发态问题相当成功的理论方法。将Hartree-Fock(HF)理论与LDA相结合,但采用非局域屏蔽交换代替HF方法中的局域非屏蔽交换相互作用,建立广义的KS方程(GKS),得到所谓屏蔽交换局域密度近似(sX-LDA)方法。我们在平面波自洽场方法PWscf程序包的基础上,发展了PW scf-sX-LDA方法,也是处理激发态问题及材料设计的有效方法。将评述激发态过程多体理论各种方法的发展和意义,讨论这些多体理论方法之间的联系和差异,并在此基础上介绍它们在解决半导体带带跃迁(或带隙偏小问题)、半导体及其微结构中的激子效应等重要领域的应用和成果。     

椭圆偏振光测不准原因分析

在光学实验中,用GSZF-3实验系统检测椭圆偏振光时,测得的振幅与角度在极坐标中画出的并不是椭圆,而是一个类肾脏线。本文分析了产生的原因,并提出了改进建议。     

下岗--再就业问题的优化

综合考虑企业与社会的总体利益,根据经济学原理,建立下岗—再就业率的优化模型,对再就业工程问题的解决有参考价值.