Elastic and thermodynamic properties of c-BN from first-principles calculations

The elastic constants and thermodynamic properties of c-BN are calculated using the first-principles plane wave method with the relativistic analytic pseudopotential of the Hartwigen, Goedecker and Hutter (HGH) type in the frame of local density approximation and using the quasi-harmonic Debye model, separately. Moreover, the dependences of the normalized volume V/V₀ on pressure P, as well as the bulk modulus B, the thermal expansion α, and the heat capacity C_V on pressure P and temperature T are also successfully obtained.     

Electronic and optical properties of the zinc-blende structured LiZnN under pressure

The electronic and optical properties of the cubic zinc-blende (ZB) structured filled tetrahedral semiconductor α-LiZnN under pressure are investigated by using \textit{ab initio} plane wave pseudopotential density functional theory method within the generalized gradient approximation (GGA). The electronic band structure and the density of state under pressure are systematically described. The basic optical constants, including the reflection and absorption spectra, the energy-loss function, the complex refractive index and the dielectric function, are calculated and analysed at different external pressures. Our results suggested that the ZB α-LiZnN is transparent in the partially ultra-violet to the visible light region, and it seems that the transparency is hardly affected by the pressure.     

A Theoretical Study of a Single-Walled ZnO Nanotube as a Sensor for H_2 O Molecules

We have studied the property of single-walled ZnO nanotubes with adsorbed water molecules, and theoretically designed a new sensor for detecting water molecules using single-walled ZnO nanotubes using a combination of density functional theory and the non-equilibrium Green's function method. Details of the geometric structures and adsorption energies of the H 2 O molecules on the ZnO nanotube surface have been investigated. Our computational results demonstrate that the formation of hydrogen bonding between the H 2 O molecules and the ZnO nanotube, and adsorption energies of the H 2 O molecules on the ZnO nanotube are larger than the adsorption energies of other gas molecules present in the atmospheric environment. Moreover, the current-voltage curves of the ZnO nanotube with and without H 2 O molecules adsorbed on its surface are calculated, the results of which showed that the H 2 O molecules form stable adsorption configurations that could lead to the decrease in current. These results suggest that the single-walled ZnO nanotubes are able to detect and monitor the presence of H 2 O molecules by applying bias voltages.     

GaAs纳米结点电子输运性质的第一性原理计算

运用密度泛函理论结合非平衡格林函数的方法,对GaAs团簇与两半无限Au(100)-3×3电极以顶位对顶位、顶位对空位、空位对顶位、空位对空位四种不同耦合形貌构成的Au-GaAs-Au纳米结点电子输运性质进行了理论计算.对结点在不同距离下的结构进行了几何优化,模拟了结点拉伸直至断裂的过程.计算结果得到四种构型结点在两极距离分别为1.389 nm,1.145 nm,1.145 nm,0.861 nm时,结构最稳定.对于各稳定结构,Ga-As键长分别为0.222 nm,0.235 nm,0.227 nm,0.235 nm,其平衡电导分别为2.33 G0,1.20 G0,1.90 G0,1.69 G0,结点具有很好的电子输运性质.在-1.2—1.2 V的电压范围内,所有结点的电流-电压都表现出近线性关系.     

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1.90 ?,B-Mg键长为2.22 ?时,结合能最大,结构最稳定,此时结点平衡电导为0.51G₀ (G₀=2e²/h)．通过计算投影态密度发现电子通     

First—Principle Calculations for Scanning—Tunelling—Microscopic Images of a Monolayer Graphite Surface

We have applied first-principle total-energy electronic structure calculations in the local density approximation to calculate the scanning tunnelling microscopy images of a monolayer graphite surface near the Fermi level.The results obtained agree well with the observation.which has not been interpreted before.     

冲击波加热的氩气的发射光谱

为了研究弱冲击条件下氩气的辐射特性,从二级轻气炮发射的89 W飞片以2.00 km/s的速度撞击封装有常态下氩气的LY12铝靶,用六通道瞬态高温计和示波器记录到受一次冲击压缩的氩气的光辐射信号随时间的变化规律:从405 nm到700 nm的5个通道信号为直线段,800 nm通道的信号为指数曲线段,并测量出相应的冲击波速度为4.10±0.09 k m/s.实验表明,冲击压缩的氩气对可见光的吸收系数较小,气体的光学厚度沿长波方向从光学薄向光学厚转变.二次冲击压缩氩气的辐射信号上升前沿的时间分辨光谱用OMA系统记录,并观察到450 nm附近有较强的发射光谱带,但没有观察到明显的线状光谱.通过冲击波后参数和氩气电离度的理论计算,解释了冲击压缩下氩气的发射光谱特性.     

重水分子伸缩振动谱的非线性量子理论计算

用非线性量子理论中的离散自陷方程对蒸汽态和液态重水分子在高激发态下的伸缩振动能谱进行了计算。从中发现重水分子的振动能谱分布具有许多有趣的特点。计算所得到的结果对研究重水在高压状态下的特性具有重要的应用价值。     

Time-Dependent Local Density Approximation Calculations for Absorption Spectra of Small Carbon Clusters

Absorption spectra for Cn clusters (n = 2-8) are calculated using an adiabatic time-dependent density functional formalism within the local density approximation (TDLDA). We compare the calculated spectra with those computed using a simple local density approximation approach. It is readily observed that the TDLDA spectra display a significant blue shift with respect to the Kohn-Sham eigenvalue spectra. The calculated spectra exhibit a variety of features that can be used for comparison against future experimental investigations. We also obtain a significant threshold absorption, which can distinguish different ground states of the carbon clusters.     

高压下金属铌熔化曲线的分子动力学模拟

铌作为一种高熔点的金属,广泛应用于制作合金材料. 铌的高温高压熔化曲线对于铌基合金的实际应用具有重要影响,但目前还未被成功研究. 本文中,我们采用铌目前已有的嵌入原子相互作用势函数（EAM）,通过经典的分子动力学方法,模拟了铌的熔化曲线. 两相法和改进Z方法的熔化曲线几乎完全一致,与Z方法的结果稍有差异. 我们也比较了尺寸效应对铌熔化曲线的影响. 我们认为,铌的现有的势函数描述其高压特性时不再适合,后续需要构建精确的温度和压强依赖的相互作用势函数来研究铌的高压特性.