Au-MgB2-Au纳米结点的负微分电阻效应

运用密度泛函理论结合非平衡格林函数的方法对MgB2直线原子链与两半无限Au（100）电极构成纳米结点的电子输运特性进行了第一性原理计算．在模拟Au-MgB2-Au纳米结点的拉伸过程中,计算了结点在不同距离下的结合能与电导．结果发现结点的Au-B键长为1．90A,B-Mg键长为2．22A时,结合能最大,结构最稳定,此时结点平衡电导为0．51G0（G0=2e^0／h）．通过计算投影态密度发现电子通过结点时主要是通过B、Mg原子的px和py电子轨道形成的π键进行传输的．在-1．5～1．5V的电压范围内,结点的电流-电压近似为线性关系,表现出类似金属的导电性质,而当正负电压高于15V时,电流对称性逐渐减小,即存在负微分电阻效应,从不同电压下透射谱的变化对负微分电阻现象进行了分析与讨论．     

First-Principles Calculation for the Electron-Phonon Coupling Constant of Superconducting MgB2

We use a first-principles plane wave method with the new relativistic analytic pseudopotential of the Hartwigsen,Goedecker and Hurter (HGH) scheme and the pseudopotential of the Troullier-Martins scheme to calculate the eleetron-phonon coupling constant λ of superconducting MgB2. The calculated results show that there is a peak at about 300-350cm^-1 in the eleetron-phonon spectral functional α2F(ω), duo to the coupling of the electrons to the acoustic phonon, and the relativistic effect appears in the high frequencies zone. All the results agree well with the present and previous experimental data,     

First-Principles Calculations of Elastic Constants of Superconducting MgB2

The five independent elastic constants of superconducting MgB2 are obtained using the first-principles plane wave method with the new relativistic analytic pseudopotential of the Hartwigsen-Goedecker-Hutter (HGH) scheme in the frame of local density approximation. The dependences of bulk modulus on temperature and pressure are also obtained. It is suggested that the HGH-type pseudopotentials are successful in investigating the ground-state mechanical properties of any solids.     

Parkinsonian oscillations and their suppression by closed-loop deep brain stimulation based on fuzzy concept

This paper provides an adaptive closed-loop strategy for suppressing the pathological oscillations of the basal ganglia based on a variable universe fuzzy algorithm. The pathological basal ganglia oscillations in the theta (4-9 Hz) and beta (12-35 Hz) frequency bands have been demonstrated to be associated with the tremor and rigidity/bradykinesia symptoms in Parkinson's disease (PD). Although the clinical application of open-loop deep brain stimulation (DBS) is effective, the stimulation waveform with the fixed parameters cannot be self-adjusted as the disease progresses, and thus the stimulation effects go poor. To deal with this difficult problem, a variable universe fuzzy closed-loop strategy is proposed to modulate different PD states. We establish a cortico-basal ganglia-thalamocortical network model to simulate pathological oscillations and test the control effect. The results suggest that the proposed closed-loop control strategy can accommodate the variation of brain states and symptoms, which may become an alternative method to administrate the symptoms in PD.     

锂原子基态能级的近似计算

将锂原子三电子哈密顿量H分解为H0(类氦锂离子与氢原子哈密顿量之和)与H′(微扰项),用微扰法计算体系的能量．在计算E0时涉及类氦锂离子能量,计算类氦锂离子能量时我们像求氦原子能量一样使用变分法,同时对计算结果作了讨论。     

分子体系的热运动基本方程

宏观热现象是由宏观物体中大量微观粒子(原子、分子…等)相互作用产生的无规则混乱运动引起的.分子体系的温度愈高、体积愈大,它的混乱运动程度就愈大,我们引入一个物理量S来表征这种运动的混乱度. 我们可以看出,混乱度S是温度T和体积V的函数S(T,V),或为能量E和体积V的函数S(E,V).我们在本文中证明,在缓慢的可逆热运动过度中,通过作微观的功和宏观功的方法,给体系一无穷小的能量dE,使其混乱度与体积的变化分别为dS与dV,则三者有如下关系:dE=TdS-pdV.这就是在可逆过程中的热运动基本方程,也就是传统热力学中所称的热力学基本方程.     

再谈任意循环极限效率的p-V图证明

在ｐ－Ｖ图上用外切卡诺循环的方法证明任意循环的极限效率更为简单明了．     

小碳团簇结构的从头算分子动力学模拟

引入第一原理密度泛函理论, 即赝势密度泛函在实空间的有限差分方法和朗之万分子动力学退火技术, 对碳团簇Cn(n=2-8)的基态结构进行了理论计算, 所得结果与其他作者的计算结果及实验数据吻合较好.     

Structural and thermodynamic properties of AlB2 compound

We employ a first-principles plane wave method with the relativistic analytic pseudopotential of Hartwigsen, Goedecker and Hutter (HGH) scheme in the frame of DFT to calculate the equilibrium lattice parameters and the thermodynamic properties of AlB₂ compound with hcp structure. The obtained lattice parameters are in good agreement with the available experimental data and those calculated by others. Through the quasi-harmonic Debye model, obtained successfully are the dependences of the normalized lattice parameters a/a₀ and c/c₀ on pressure P, the normalized primitive cell volume V/V₀ on pressure P, the variation of the thermal expansion α with pressure P and temperature T, as well as the Debye temperature \Theta_D and the heat capacity C_V on pressure P and temperature T.