硅团簇的结构及生长模式——紧束缚分子动力学：Si11—Si32

采用紧束缚分子动力学模拟硅团簇的结构，通过比较它们的结合能来确定基态结构，最后描绘出不同尺寸所对应的径向分布函数、角分布函数.模拟表明硅团簇在n=27处发生结构转变，从结构图上看，是由扁长结构向近球形结构转变.从径向分布函数图像、键角分布函数图像上也可以得到团簇结构在n=27处发生了变化，结构变得越来越紧密. 关键词： 硅团簇 紧束缚分子动力学 模拟退火 基态结构     

低温下Au959团簇负载于MgO(100)表面后结构变化的分子动力学研究

采用基于Chen-Mbius反演方法,从金属/金属氧化物界面第一性原理计算的粘结能结果中推导出的Au/MgO原子间相互作用势的正则系综（NVT）分子动力学,模拟了在10 K条件下,Au₉₅₉团簇负载于MgO（100）表面后团簇结构的变化.根据原子对分析技术和对分布函数的分析表明,由于团簇界面处原子间距与载体原子间距相匹配,置于载体上的Au团簇经过一个变形过程后,较其孤立自由表面时的团簇体积变大. 关键词： 团簇 分子动力学 计算机模拟 表面     

Na5, Na6和Na7团簇光学吸收谱的理论研究

以含时密度泛函理论为基础，结合从头赝势方法运用含时局域密度近似计算了Na₅，Na₆和Na₇团簇的动力学极化强度，并通过傅里叶变换得出了团簇的光学吸收谱.研究表明，计算结果可以较好地再现实验谱，而且Na₆和Na₇团簇的结果和组态相互作用的结果符合较好.二维结构和三维结构的Na₆团簇的计算结果表明，只有二维结构可出现低于2 eV以下的峰，而且二维结构光谱的计算结果与实验结果符合较好. 关键词： 光吸收谱 Na团簇 含时局域密度近似     

纳米铜团簇凝结规律的分子动力学研究

采用分子动力学方法对包含147，309和561个原子数的液态纳米铜团簇凝结过程进行模拟研 究，结果表明降温速率及团簇原子数对凝结得到常温下的固态团簇结构有重要影响：在模拟 时间内，降温速度越慢，团簇原子数越少，凝结得到铜团簇越倾向生成二十面体结构，反之 则倾向生成面心立方结构.同时探讨了该现象的物理机理. 关键词： 铜团簇 凝结 结构 分子动力学     

AuCu249合金团簇热稳定性的原子尺度计算研究

采用基于嵌入原子法的NVT正则系综分子动力学方法,在原子尺度上计算了包含249个原子的金属间化合物AuCu₂₄₉合金团簇由固态转变为熔体的结构演化过程. 根据对分布函数、原子密度分布函数和主要原子键对数目随温度的变化,发现在温度从低温升到高温的过程中,合金团簇内伴随着原子的连续位置交换,团簇呈现由外及里的分阶段结构转变. 同时还发现在团簇内原子堆积结构转变过程中,Au原子出现由团簇内层向外层运动的趋势,而Cu原子则有由外层向内层运动的趋势. 关键词： 合金团簇 分子动力学 计算机模拟 相变     

团簇的第一原理分子动力学计算研究：价键优选法

根据团簇价键结构的特点，结合第一原理分子动力学模拟，提出价键优选法；可以在有限的 计算量之下，得到其可计算的最大团簇体系Xm的性质，以及所有团簇Xi(i关键词： 价键优选法 团簇 第一原理分子动力学 Jahn_Teller效应 Rennet_Teller效应     

LJ团簇和H2O团簇的局域优化计算

将传统分子动力学方法中时间积分步长定义成粒子的最大加速度、最大速度和变化的最大允许空间步长的函数,并给出了空间步长的确定方法.作为对这个算法有效性的检验,计算了较小Lennard-Jones团簇和H₂O团簇的稳定结构,发现了新的(H₂O)₁₃的最小能结构.     

BaTiO3晶体结构及弹性的分子动力学模拟

有效的势函数是分子动力学模拟的关键. 引入了一种势函数,该势函数的特点是运用参数r_eff计算原子间的静电作用. 通过分子动力学方法模拟得到了BaTiO₃晶体立方相、四方相结构的对关联函数和X射线衍射谱,计算得出了它们的晶格常数及弹性常数. 模拟结果与实验结果符合较好.该势函数可以有效地模拟BaTiO₃晶体的热学和力学性能. 关键词： 分子动力学模拟 势函数 3铁电晶体')" href="#">BaTiO₃铁电晶体     

团簇异构体生长概率的理论预测

由于实验表征团簇结构的困难,理论预测团簇在生长过程中各种异构体的生成概率便十分重要.考虑到分子动力学可模拟高温时各异构体的相对丰度,把问题归结为高温时所形成的各种异构体在室温环境中如何转化,并建立了统计力学模型,得到了异构体相互演化所需时间与环境温度的解析关系.以C₁₂团簇为例,在2500 K时所形成的最可几异构体在室温环境中需要超过10¹²年才能转化为最低势能异构体. 关键词： 团簇 异构体 统计物理 分子动力学     

金属钛中氦团簇生长行为的分子动力学研究

运用分子动力学方法模拟了常温下金属钛中氦团簇的生长过程.从能量的角度考察了氦团簇的生长机理.研究发现,随着氦团簇的生长,在氦团簇周围逐渐形成位错环缺陷,氦团簇与氦原子的结合能有逐渐下降的趋势,当氦团簇生长到一定尺寸时会通过发射周围缺陷以使得结合能上升,从而增强了进一步吸收氦原子的能力.模拟还发现,随着氦团簇的继续生长,氦团簇的形状由原来的不规则结构逐渐变成了较为规则的棱柱形结构,在随后的生长过程中其生长仅在（001）平面进行,沿［001］轴的厚度几乎不变. 关键词： 氦团簇 缺陷发射 分子动力学模拟     

Molecular dynamics calculations of anharmonic properties of the vibrational spectrum of BCC zirconium under pressure

The structural stability and lattice dynamics of the high-pressure bcc phase of Zr at a constant temperature T = 500 K are studied for various volumes using molecular dynamics simulation with the Animalu pair pseudopotential. Dispersion curves of the vibrational spectrum calculated by the molecular dynamics method for various volumes are compared to the phonon spectrum obtained in the harmonic approximation. It is demonstrated that, as the volume decreases, all frequencies of the vibrational spectrum increase gradually and bcc zirconium remains strongly anharmonic along all high-symmetry directions of the Brillouin zone over the entire range of volumes studied. The strongly anharmonic N _T1 phonon is significantly softened near the point of structural instability of bcc-Zr at T = 500 K and V = 0.87V ₀. As the volume decreases to V = 0.73V ₀ under pressure, the anharmonic corrections for this phonon decrease by almost an order of magnitude and the phonons near the H point of the Brillouin zone become anharmonic. The damping of the T ₁ phonon mode along the [110] direction is calculated as a function of pressure.     

A molecular dynamics simulation of the destruction of explosive molecules at high-velocity collisions

The infrared spectra and the energies of dissociation of R-NO₂ bonds (R≡C, N, and O) were calculated for explosive molecules (trinitrotoluene, hexogen, octogen, pentaerythrityl tetranitrate, triaminotrinitrobenzene, and nitromethane). The time of kinetic energy redistribution over intramolecular vibrational modes for these molecules (the V-V relaxation time) was calculated by the molecular dynamics simulation method. Molecular dynamics simulations were also used to model the collision-induced destruction of hexogen, octogen, and tri-nitrotoluene molecules. The threshold velocities of collisions at which the destruction of molecules took a time shorter than the V-V relaxation time were determined.     

Experimental studies of the magnetic excitations in the 1D Ising-antiferromagnet CsCoCl3

The electronic Raman and infrared absorption spectrum within the ⁴T_1g ground term of the one dimensional antiferromagnet CsCoCl₃ is investigated. At 2K three magnon lines are observed whereas above the magnetic phase transition at 8K the number of lines is increased to twelve. No drastic change of the magnon spectrum is observed in passing the Neél temperature at 21.5K. The magnon spectrum could still be observed at 150K. Theoretically the one-exciton spectrum is described within the molecular field approximation, using an exchange coupling between nearest neighbours along the spin chains only. Satisfactory agreement is obtained between measured and calculated energies.     

Electronic structure of the SiAu surface

The electronic density of states of the SiAu surface is calculated using a continued fraction technique. The geometric structure of the surface alloy Au₄Si is generated by molecular dynamics. The local density of states on Si atoms in a metallic environment differs qualitatively from the sp spectrum of a typical semiconductor. The calculated densities of p states of Si are in good agreement with recent X-ray spectra of Si in a metallic environment.     

High resolution infrared spectrum of silane

The infrared absorption spectrum of SiH₄ in the 4200–4500 cm^?1 region has been recorded using a high resolution grille-spectrometer. Two bands have been observed and identified as 2ν₃ and ν₁ + ν₃. Some molecular constants have been calculated, using the formalism developed by Jacques Moret-Bailly.     

CuA1S2 crystalline lattice dynamics

Using the model of rigid ions bound by short-distance forces the lattice dynamics of the CuA1S₂ crystal with chalcopyrites structure are investigated. The model parameters are determined from experiments on infrared reflection and combination scattering of light. The phonon spectrum is calculated in the center of the Brillouin zone and in directions of high symmetry. Oscillator amplitudes for frequencies active in IR reflection and components of the static dielectric permeability tensor are calculated.     

High-resolution infrared spectrum and rovibrational analysis of the ν3 fundamental of diazirine,H213CN2

The high-resolution infrared spectrum of ¹³C-diazirine was recorded using a high-information Fourier transform spectrometer with a resolution of 0.0054 cm^?1. The rovibrational structure of the ν₃ fundamental at 1458.1884 cm^?1, which is an A-type parallel band (¹³CH₂ deformation) was assigned and analyzed with extensive use of modern methods of spectrum simulation. The rovibrational assignment and the molecular constants determined for the excited vibrational level of this band are given.     

The ν9 band of diazirine,H2CN2, by Doppler-limited Fourier transform infrared spectroscopy

The Doppler-limited infrared spectrum of diazirine was recorded using a high-information Fourier transform spectrometer with a resolution of 0.0054 cm^?1. The rovibrational structure of the ν₉ fundamental (CH₂ rocking) at 1124.9144 cm^?1, which is a C-type band, was analyzed in detail with extensive use of spectrum simulation and correlation diagrams. The molecular constants for the upper energy level of this band were obtained from the overall rovibrational assignment of more than 2000 transitions, which cover the region from 1070 to 1220 cm^?1.     

Radiative and nonradiative recombination of self-trapped exciton on silicon nanocrystal interface

The theory of the multiphonon and radiative recombination of a self-trapped exciton on the interface of a silicon nanocrystal in a SiO₂ matrix is developed. Self-trapped excitons play a key role in the hot carrier dynamics in nanocrystals under photoexcitation. The ratio of the probabilities of the multiphonon and radiative recombination of the self-trapped exciton is estimated. The probabilities of exciton tunnel transition from the self-trapped state to a nanocrystal are calculated for nanocrystals of various sizes. The infrared range spectrum of the luminescence of the self-trapped exciton is obtained.     

Lattice dynamics,thermodynamic and elastic properties of CdGeAs2

Summary An extended Keating’s model with two-bond-stretching and one-angle-bending force constants within the rigid-ion approximation is applied to the investigation of the lattice dynamics of CdGeAs₂. Five model parameters of the theory are determined by a least-square fitting to the infrared reflectivity measurements. The phonon spectrum along two high-symmetry directions and the one-phonon density of states are calculated. The theoretical values of the elastic constants, the constant-volume specific heat and the Debye temperature show a reasonable agreement with the experimental data reported by other authors.