Cu(100)表面吸附CN的密度泛函研究

采用密度泛函方法，以原子簇Cu14为模拟表面，对CN自由基分子在垂直和平行Cu(100)表面不同位置的吸附情况进行了研究，结果表明：通过原子C垂直吸附在表面的顶位是其最佳吸附方式，吸附后CN键振动频率发生蓝移；而其它吸附方式中CN键振动频率均发生红移．DOS和电荷转移分析指出CN通过C端吸附在表面顶位位置时，Cu与CN之间具有较强的σ成键和较弱的π反键特征．     

Si5H3,Si5H6,Si5Li3及Si5Na3原子簇结构的理论研究

利用Gaussian-94计算程序中的B3LYP方法，在6—311 G(2d)6d基组下，对Si5，Si5H3，Si5H6，Si5Li3和Si5Na33原子簇的几何结构进行优化和频率计算．结果表明，Si5原子簇中最稳定的具有D3h对称性的结构中，位于同一平面上的3个Si原子确实具有剩余的成键能力，可以与3个H，Li，Na原子和6个H原子形成稳定的化合物．研究还发现，虽然H，Li和Na都属同一主族，但它们与Si5原子簇中Si原子的键连方式却不同，而且它们的加入，对Si5原子簇的“三角双锥”结构也有不同的影响．     

多体展形势函数在碳族元素原子族研究中的应用（Ⅳ）—Si9—Si16原子簇…

多体展开势能函数研究表明，Ｓｉ４－Ｓｉ１６原子簇分子间的结构衍生关系：依次增加一个二配位或三配位的表面原子，分子表面被四元蝶形环Ｓｉ４（Ｄ２ｄ）所覆盖；Ｓｉｎ（ｎ＝５－１６）结构中多含有Ｓｉ５（Ｄ３ｈ）、Ｓｉ６（Ｄ２ｄ）区域结构单元，笼状Ｓｉ１０及Ｓｉ１６的表面原子均为三配位或三配位以上，预计Ｓｉ５、Ｓｉ６、Ｓｉ１０及ｓｉ１６是硅原子簇碎片化产物分布中丰度较高的序列；在这一范围内的分子结构呈与晶体     

苯在Si(111)-7*7表面化学吸附的理论研究

采用两种大小不同的原子簇模型Si_(30)H_(28)和Si_(13)H_(16)，分别用两层 ONIOM方法（对较大原子簇）和普通量子化学方法（对较小原子族）考察了苯分子 在Si(111)-7 * 7表面的化学吸附。对三种可能的吸附物种分别用DFT或HF方法进行 了计算。通过大小原子簇吸附物种的吸附能以及几何构型优化参数的比较发现，对 于稳定的吸附物种，较小的原子簇基本上可以代替较大的原子簇进行计算，而对于 不太稳定的吸附物种，就不得不考虑周边原子的影响。计算结果表明苯在Si(111)- 7 * 7表面的主要吸附种是双σ成键的1，4加成产物，不稳定的单吸附物种可能是 1，4加成物种的前驱态。     

CO在Ni表面甲烷化反应的CNDO/2研究

本文用CNDO/2方法,选择Ni_5、Ni_6原子簇模拟Ni(100)的三个典型位置,对CO的吸附情况和CO在Ni表面解离为活性碳原子的方式进行了研究,进而探讨了甲烷化反应的机理。     

苯在Si(111)-7×7表面化学吸附的理论研究

采用两种大小不同的原子簇模型Si_(30)H_(28)和Si_(13)H_(16)，分别用两层 ONIOM方法（对较大原子簇）和普通量子化学方法（对较小原子族）考察了苯分子 在Si(111)-7 * 7表面的化学吸附。对三种可能的吸附物种分别用DFT或HF方法进行 了计算。通过大小原子簇吸附物种的吸附能以及几何构型优化参数的比较发现，对 于稳定的吸附物种，较小的原子簇基本上可以代替较大的原子簇进行计算，而对于 不太稳定的吸附物种，就不得不考虑周边原子的影响。计算结果表明苯在Si(111)- 7 * 7表面的主要吸附种是双σ成键的1，4加成产物，不稳定的单吸附物种可能是 1，4加成物种的前驱态。     

Cu(100)表面吸附HCN和HNC的密度泛函研究

采用密度泛函方法，以原子簇Cul4为模拟表面，对氢氰酸(HCN)和异氰酸(HNC) 在Cu(100)表面上不同吸附位的吸附情况进行了研究．结果表明：HCN和HNC分别通 过原子N和C垂直吸附在表面上时，顶位是其最佳吸附位，且是吸附能为18．5kJ· mol^-1和42．6kJ·mol^-1的弱吸附，计算结果与实验相符．C—N(HCN)键或N—C (NHC)键偏离垂直的分子轴线的吸附体系均不稳定．顶位吸附时HCN和HNC分子的C- N键振动频率均发生蓝移．     

硅烷热分解制备硅原子簇

当前，半导体硅原子簇的物理与化学性能已成为人们广泛研究的热点[1]．尽管近几年来硅原子簇研究取得很大进展，但对于大于10个原子的硅原子簇的实验及理论研究尚很少见[2]．目前，均采用在超高真空系统中，利用脉冲激光蒸发硅棒获得硅原子簇，然后进行分析．检测及化学反应研究，还不能离开真空系统．为此，发展一种能够制备可观量的、在大气中稳定的原子簇的方法很有必要．我们利用硅烷热分解的化学方法，制备硅原子簇工艺，如图1所示．采用MO丝加热，以Ar气稀释SM。气体，为防止气管喷嘴在反应中被产物堵塞，使用了Cap2保护，控制温度…     

升温速率对金属铅的熔化和过热行为的影响

采用分子动力学方法和QSC(quantum Sutton-Chen)力场研究了升温速率对金属铅的熔化和过热行为的影响.模拟中考虑了缺陷和表面对熔化和过热行为的作用.结果表明，升温速率对金属铅的熔化和过热行为影响很大，随着升温速率的升高，金属铅的熔点有所升高.快的升温速率会导致金属铅体系内部无序化程度增加，进而使体系能量增加，降低了熔化相变的能垒.升温速率导致的金属铅的过热极限大约为780 K.     

金属Cu低指数表面熔化行为的分子动力学模

采用Mishin镶嵌原子势, 通过分子动力学方法模拟了金属Cu的低指数表面在不同温度的表面熔化行为, 分析了熔化过程中系统结构组态的变化以及固-液界面迁移情况. 金属Cu的(100)和(110)表面在低于熔点发生预熔化, 而(111)表面存在明显的过热现象. 准液体层的厚度随温度升高而增加, 热稳定性与表面的密排顺序一致, 按(111)、(100)、(110)顺序增大. 当温度高于热力学熔点时, 固液界面的移动速度与温度成正比, 外推得到热力学熔点约为1360～1380 K, 与实验结果1358 K吻合良好. 动力学系数定义为界面移动速度与过热程度的比值, 表现为明显的各向异性: k100=39 cm•s−1•K−1, k110=29 cm•s−1•K−1, k111=20 cm•s−1•K−1. k100与k110之间的比例符合collision-limited理论, (111)密排面有与其它低指数表面不同的熔化方式.     

Melting of Lennard-Jones clusters in confined geometries

The melting of Lennard-Jones (argon) clusters of various size (N = 500 to 10000 atoms), confined in a rigid matrix, is studied by molecular dynamics simulations. For spherical clusters we show the existence of a cluster size below which the dependence of the melting temperature cannot be described by the classical Gibbs-Thompson equation. We also provide evidence of the formation of a quasi-liquid layer at the surface of mesoscopic clusters. A good agreement is found between the theoretical model due to Celestini et al. and the simulation results obtained in this work. The melting of an ellipsoidal cluster is also investigated. We observe, in agreement with recent experimental and theoretical work, that the thickness of the molten layer is larger in the region of higher local curvature.     

A molecular dynamics simulation of rebound,capture and diffusion in collisions at thermal energies between a rare gas atom and an argon cluster (n=125)

Molecular dynamics calculations have been performed to simulate the low energy collision (0.2 eV) of a rare gas atom (He, Ar, Xe) with a cluster of 125 argon atoms. Depending on its relative mass to argon, the projectile is either deflected (He) or captured (Ar, Xe) by the argon cluster. We have determined the deflection function of the He projectile that is scattered, and for Xe we have determined wether it stays near the surface of the cluster or migrates inside. These results have been discussed in the light of very simple models.     

Ejection of cluster ions as a result of electron impact ionization of argon clusters

Time evolution of mass distribution of argon cluster ions has been studied in pulsed jets (pulse duration≈0.4 ms) by retarding potential method. The ejection of cluster ions of the order of 180 atoms from cluster ions of the order of 500 atoms has been revealed. The ejection has a threshold character as a function of the time elapsed after electron impact ionization. The threshold time was about 20 μs. Delayed non-thermal fragmentation of the cluster ions testifies that the self-trapped ion, formed in argon clusters as a result of ionization, can live for a long time in its excited state without dissipation of the excess energy to the cluster. This ion should be located on the surface of the cluster. Energetic analysis of the fragmentation is consistent with the size of the ejected clusters. A model of the observed time evolution of the delayed fragmentation is herein proposed.     

Preferential site occupancy of krypton atoms on free argon-cluster surfaces

Argon clusters have been doped with krypton atoms in a pick-up setup and investigated by means of ultraviolet and x-ray photoelectron spectroscopy (UPS and XPS). The width of the krypton surface feature in the XPS spectra from mixed krypton/argon clusters has been studied and found to be narrower than in the case of homogeneous krypton clusters. By considering known spectral broadening mechanisms of the cluster features and the electron binding energy shift of the cluster surface feature relative to the atomic signal, we conclude that krypton ad-atoms preferentially occupy high-coordination surface sites on the argon host-cluster.     

IR spectra of aqueous disperse systems adsorbing atmospheric gases: 2. Argon

The absorption, reflection, and scattering of IR radiation by aqueous ultradisperse systems that absorb argon are studied with the molecular dynamics method on the basis of a flexible molecule model. Both the real and imaginary parts of dielectric permittivity are substantially increased at frequencies corresponding to intramolecular vibrations of atoms when each cluster of aqueous system adsorbs one argon atom. This effect disappears for the real part and becomes weak for the imaginary part of dielectric permittivity when there are two argon atoms added per cluster. In the region of intramolecular frequencies, the absorption coefficient of aqueous disperse systems containing argon increases as well. The reflection coefficient of the systems of water clusters that absorbed argon decreases in the frequency region of vibrations of molecules and increases in a frequency range corresponding to intramolecular vibrations. The power of radiation generated by cluster systems at the expense of thermal energy increases considerably when there is one adsorbed argon atom per cluster and decreases with a twofold increase in the number of argon atoms in clusters.     

中介尺度Au纳米团簇熔化的分子动力学模拟

采用分子动力学模拟技术，研究了原子个数为16～8628的 Au纳米团簇的熔化过程.采用 Johnson的EAM (embedded atom method) 模型,模拟结果表明，金属纳米团簇存在一中介尺度区域.对Au纳米团簇而言，当原子个数N >456时，团簇的热力学性质与团簇尺寸呈线性关系，熔化首先从表面开始，逐步向中心区域推进，且满足Tmb－Tmc(N)＝aN(－1/3)的关系.另外，计算了中介区域的团簇的尺寸、熔化温度、表面能、熵、焓等热力学量以及均方根位移（RMSD）等动力学量，为研究纳米团簇提供定量数据.     

Melting of icosahedral gold nanoclusters from molecular dynamics simulations

Molecular dynamics simulations show that gold clusters with about 600-3000 atoms crystallize into a Mackay icosahedron upon cooling from the liquid. A detailed surface analysis shows that the facets on the surface of the Mackay icosahedral gold clusters soften but do not premelt below the bulk melting temperature. This softening is found to be due to the increasing mobility of vertex and edge atoms with temperature, which leads to inter-layer and intra-layer diffusion, and a shrinkage of the average facet size, so that the average shape of the cluster is nearly spherical at melting.     

Spontaneous coalescence in ultrafine metal particle aggregates

In the preparation of ultrafine metal particles (Cu, Ti, Ni or Al) by opposed-targets dc sputtering, a substrate cooled by liquid helium flow was used, on which the metal clusters and argon atoms were condensed simultaneously, forming a solid layer of the mixture. By raising the temperature of the substrate and the argon pressure in the chamber, the solid argon melts and evaporates, remaining the metal-particle aggregates. After complete evaporation of the argon, a phenomenon was observed in which the metal-particle aggregates shrank and suddenly changed their colour from black to bulk-metal colour, followed by an explosion-like noise. We offer an explanation for this phenomenon by the mechanism of spontaneous coalescence due to the large surface energy of the ultrafine particles. From our observation and analysis, we conclude that a certain particle size exists, below which the spontaneous coalescence may occur in a very fast way, leading to melting of the particles. The fast process of coalescence, melting and cooling introduces large internal stress which splits the sintered particle, giving the explosion-like noise. This phenomenon may imply a size limitation in forming nanocrystalline solid materials of pure metals.     

Argon–water system at low temperatures

The molecular dynamics method is used to simulate argon solutions in water and a thin water film–argon system at low temperatures. The correlation in motions of two closely spaced argon atoms is of another nature than the correlation of two neon atoms in a neon solid solution in ice II. The structure of hydrate shells of argon atoms contains five-membered rings composed of water molecules. The solubility of argon in a water film at low temperatures is noticeably higher than at room temperature. If a water film is first cooled to the glassy state and then argon atoms are added to it, then approximately as many argon atoms are absorbed on the film surface as they are present in a cooled film in equilibrium with the argon atmosphere. Argon atoms migrate from one pit to another on the rough surface of a solid water film.     

Isotopic effect on the cage-induced quenching of OH(A)/OD(A) inside small argon clusters

In this paper we report on the isotopic effect on the cage-induced excited-state quenching inside small Ar(m) clusters (m<10(2)) solvated in large Ne(N) clusters (N approximately 7.5x10(3)). Excited OH(A)/OD(A) fragments are produced by photodissociation of H2O and D2O molecules and the quenching agents are correspondingly H or D atoms. The decrease of the fluorescence yield with the size of the cluster m>m0 is observed in both cases and it is attributed to the formation of the cage of argon atoms around the doped molecule. Interestingly, more atoms are needed to induce the fluorescence quenching of OD*(A) fragments, m0=21+/-3, compared to the electronically excited state quenching of OH*(A) molecules, 11+/-2. A diffusion model containing two free parameters, the quenching cross section sigmaq and the number of argon atoms forming the cage m0, explains the effect in terms of the residence time of the hydrogen atom inside the cage. We suggest that the melting of the doped rare gas clusters is responsible for the different predissociation dynamics. The quenching cross section obtained from the experimental data is in good agreement with former experiments.