Molecular Dynamics Simulation Study Of Melting Behaviors Of Mixed Metal Clusters By Gupta Potential

In this thesis, by applying the constant temperature molecular dynamics simulation method, the melting behaviors of 15 kinds of metal clusters containing up to 2200 atoms and the segregation behaviors of the component atoms in bimetallic clusters are systematically investigated. The main research contents and results are as follows:(1) Started from five different types of initial structures(Ih, TD, Oh, CHCP, and NHCP), the dynamical stabilities of the icosahedral-like clusters containing up to 2200 atoms are investigated for 15 different kinds of metal elements. The obtained sequences of the dynamical stabilities of the icosahedral-like clusters can be classified into three types from stronger to weaker according to the size ranges involved:(Zr, Al, Ti) >(Cu, Fe, Co, Ni, Mg, Ag) >(Pb, Au, Pd, Pt, Rh, Ir), as corresponding to the predicted formation ability of the quasicrystals. The differences of the sequences can be attributed to analyze the parameters of the Gupta-type many-body inter-atomic potentials.(2) The annealing processes of the Ag-Cu bimetallic clusters with different sizes and compositions are systematically investigated by using the constant temperature molecular dynamics simulation method. Through analysing the annealing structures, the segregation behaviours of Ag atoms in the bimetallic clusters can be deduced as follows: When the proportion of Ag atoms is greatly less than Cu, Ag atoms all occupy the sites on the surface of the cluster; With the increase of the number of Ag atoms until the proportion of Ag and Cu are close to each other, the vast majority of Ag atoms are still on the surface, and this is consistent with the recent experimental observations of the segregations of Ag atoms in the Ag-Cu clusters. Through analyzing the relationships between the segregation behaviors of Ag atoms in the bimetallic clusters and the sizes, compositions as well as the temperatures of the bimetallic clusters, one can deduce that: When the proportion of Ag atoms is greatly less than Cu, the segregation temperature is always higher than the melting temperature of the cluster at all sizes, which means that the segregation behaviours of Ag atoms still occur at a temperature range higher than the melting point; When the proportion of Ag atoms is greatly larger than Cu, the segregation temperature is always lower than the melting temperature of the cluster at all sizes; When the proportion of Ag and Cu are close to each other for the cluster with comparatively large size, the segregation temperature is equal to the melting temperature of the cluster.