【作者】 王玲；

【导师】 承焕生； 宁西京；

【作者基本信息】 复旦大学 ， 粒子物理与原子核物理， 2005， 博士

【摘要】 本论文采用分子动力学方法对两方面的内容展开了研究:He在金属中的行为;金属团簇结构及生长动力学研究 1.He在金属中行为的研究 在很多领域的金属材料中存在He产生的问题,产生的He原子在金属中会迁移、聚集,形成大的He泡。He泡在金属中将破坏金属的性能,导致金属材料失效。研究He在金属中的行为,对理解He泡的形成,并最终延长相关材料的使用寿命有重要的意义。大量的工作对He在金属中的扩散机制进行了研究。常用的方法是采用静态的方法计算He在金属中的势垒,但是He原子的扩散常发生在非平衡的体系下,仅仅通过静态势垒计算来猜测He在金属中的行为是不够的,但相关动力学过程的报道并没有见到。 本文工作主要围绕储氚材料中氚衰变产生的He原子在金属中的行为展开的,采用分子动力学方法对He在金属Cu中的动力学行为进行了探索,给出了由T衰变产生He原子在金属Cu中迁移的动力学图景。结果表明在氚衰变初期,局域温度升高,品格发生形变;在无缺陷的Cu晶体中,单个He原子在金属中以间隙位迁移,He原子在金属中有很强的聚集趋势,而且两个He原子聚集形成的He二聚物能够挤出晶格Cu原子并占据空位。而对于有预存空位的体系,He原子将迅速占据空位,只引起很小的形变。同时通过体系势能的计算对上述现象给出了物理解释。 2.金属团簇结构及生长动力学过程的研究 金属团簇具有很多块状材料所不具备的优异特性,并有望于在合成纳米材料、器件中起到重要作用,因此金属团簇的研究受到人们广泛的关注。很多工作研究了团簇结构,团簇生长过程,团簇特性。虽然通过实验方法可以得到一些团簇结构的信息,但是它无法给出确定的团簇结构,因此各种方法的理论计算被用于结构的研究。过去人们主要通过全局优化(Global Optimization)的方法(密度泛函,蒙特卡洛和遗传算法等)致力于寻找基态结构,但是这些方法有一个明显的问题,最后的结果严重依赖于体系所赋予的初始构型,而且在结构的研究中过去更多还原

【Abstract】 In this thesis molecular dynamics method is used to investigate two contents: the He atom behavior in the metal; the structures and growing dynamics of metal clusters.1. He atom behavior in the metalIn many field there is a problem of He generated in metals. The He atoms in metals migrate, concentrate and form a large He bubble, which will destroy the property of metals and make them invalid. Investigation of He atom behavior in metal has great meaning for understanding the He bubble formation with expectation to prolong the life of the metal. Therefore lots of work have studied the diffusion mechanism of He atoms in metals. Typically the stationary method is performed to calculate the potential barrier of He in metals. However, He atom diffusion often happens in a nonequilibrium circumstance, so that only calculating barrier by stationary method is not enough. But the relevant reports on dynamical progress have not been found.This thesis focuses on the dynamics behavior of He atoms generated from T decay in metal. Molecular dynamics method is applied to explore the He atom dynamical behavior in the Cu crystal, and provides the dynamical picture of He atoms diffusion in metal Cu crystal. It is found that at the early stage just after T decay happening, the local temperature rises greatly and the crystal is deformed badly. In a perfect crystal the single He atom diffuses in the interstitial, He atoms have a strong tendency to concentrate, and thus formed He dimer can push a crystal Cu atom and occupy the vacancy. For a metal with pre-vacancy, He atoms occupy the vacancy rapidly with just a little deformation. By calculation the potential of system, we give the physical explanation for above phenomena.2. The structures and growing dynamics of metal clustersMetal clusters have many excellent properties that the bulk metals do not possess, and are promising to play a key role in the synthesis of nano material and nano equipment. So the metal clusters attract abroad attentions. Many work have been done on the structure, growing progress, and property of the clusters. Although experiments can provide some information on structures, they are failed to give unambiguous structures. Hence theoretical calculations are used to search for the ground structure, by adopting the global optimization, such as density function theory, Monte Carlo method and genetic algorithm. However, the method has an obvious problem that the results greatly depend on the initial configuration, as well as these works mainly focus on the ground structures, other than the isomers. But our previous research on the growing dynamics of carbon clusters found that the most probable is not the ground structure, and the isomers are very significant in the formation of clusters. Additionally, in the past the investigation of real dynamics, considering the buffer gas, is seldom. Hence, searching for isomers of metal clusters and the dynamics study is very important for understanding the cluster formation in the real condition.In this thesis a simple model is used to search for the isomers of metal clusters, which avoid the dependence of the results on the initial configuration in other methods. Firstly Cu cluster families for n=3-60 are obtained, and E-chart is set up according to the average binding energy. It shows that the stable clusters, compared with other clusters, have few isomers, and their structures have higher symmetry and is better closed. By comparison of isomer structures for each cluster family, the ground structure has higher symmetry and more bonds. Secondly the model is used to search for Au cluster families for n=7- 40, and compare their structures with Cu clusters. It is found that except Au^, the ground structures for the cluster families n=7-13 are same, but for the n>13, the ground structure is very different with Cu clusters with lower symmetry and worse closed, and there are more amorphous structures become more for Au isomers oFurthermore, in this thesis the growing dynamics of the metal cluster is studied. In order to overcome the problem that the calculation is too much when the buffer gas atoms are involved, a simple molecular dynamics model (SMD)-virtual thermal model, is set up, avoiding really calculating the trajectories of buffer gas atoms instead being treated as a thermal bath with temperature being a variable, which greatly saves the calculation. Using this model, we simulated developing dynamics of 100 copper atoms at different pressure of buffer gas and simulated cluster CU38更多还原