Molecular Dynamitic Method Studies He Atom Behavior In Metal, And Structural Property And Growing Dynamics Of Metal Clusters

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...