Transitions and Geometric Evolution of Cu 309 Nanocluster during Slow Cooling Process

摘要

Since the nucleation and growth of clusters is usually a non-equilibrium condensation process, a distribution of structural isomers for a given cluster size may be encountered even under the same conditions. In this work, molecular dynamics simulations are performed on sets of molten clusters of Cu 309 to study their structures at low temperatures while controlling the cooling rate. Several different final structures including perfect icosahedra (ICO), imperfect Mark’ decahedra (MDEC) and imperfect FCC truncated octahedra (TOCT) are obtained even at the same cooling rate. It is calculated that the most favorable structure is icosahedra, which becomes more and more favorable as the cooling rate is slowed. To better understand the process of crystallization, several techniques, including potential-temperature curves, common neighbor analysis (CNA) and radial distribution function (RDF), are used to analyze and study the structural transition. Results show that different structures are obtained under identical conditions due to the stochastic nature of nucleation and relatively small energy difference between isomers. The process of geometrical evolution for icosahedra is given by comparing and analyzing the time evolution of the root-mean-square deviation (RMSD) of atoms located in every shell.