Analysis Of Normal Modes Of Clusters And Study On The Melting Properties Of (AgI)₆ By Molecular Dynamics Simulation

Clusters have attracted a lot of interests in recent decades due to the characteristics of microstructure of clusters and the potential values to manufacture and develop the special materials. One of the important fields in cluster science is to study the phase transition of the cluster, which has important significance for understanding the peculiar melting behaviors of finite systems. Molecular dynamics simulation is a powerful tool to study the melting properties of clusters, which can present statistical values of thermodynamics and the movement details of atoms.In this thesis, firstly, an introduction has been given in Chapter 1, which involve the basic conception, properties and investigative significance of clusters; Chapter 2 described the molecular dynamics simulation technique; In Chapter 3, the theory of normal mode were introduced, and then the normal modes of (AgI)_n (n=2-5) clusters were studied in detail by using the program which was used to calculate the normal modes of AgI system. In the calculation, the ground state structures of the clusters were determined by using the genetic algorithm and empirical potential function. Meanwhile, the vibration of the (AgI)_n (n=2,3) clusters under every normal mode was studied. In Chapter 4, the melting behavior of (AgI)₆ was investigated using micro-canonical molecular dynamics simulation. For the small clusters, the results calculated using the molecular dynamics simulation may depend on the initial velocity distribution. In order to interpret the inconsistency between the bond length fluctuation and the heat capacity, the initial velocity was produced by the normal modes. For the special structure of the (AgI)₆, there will come forth continuous change between front face and side face of the cluster, and the faces which change from front to side for every time was indeterminacy, so the bond length fluctuation and the heat capacity interpreted inconsistency at middle temperature. On the other hand, because the simple harmonic vibration only is the approximation in small vibration, the vibration behavior of the cluster translate gradually from simple harmonic vibration to equilibrium state with the increasing of the temperature, and the initial velocity under which the vibration of the cluster is simple harmonic vibration was lost at sometime, so the melting behavior of (AgI)₆ got in different normal modes are similar to each other. In Chapter 5, some summarization and a vista of the future work have been given.