小尺寸铜团簇冷却与并合过程中结构变化的原子尺度研究

Structural changes during freezing and coalescing of small sized clusters on atomic scale

研究CuN(N=57,58,59)熔融铜团簇在冷却过程以及300K时两个具有二十面体结构Cu55团簇在并合过程中的结构变化.对这些小尺寸团簇的结构变化采用基于嵌入原子方法的正则系综分子动力学进行计算机模拟.通过对模拟结果的分析表明,小团簇的冷却和并合过程存在阶段变化的特点.降温过程中CuN(N=57,58,59)团簇的原子运动及其微观结构变化表现出较大差异,由此导致这三类团簇内原子排布的不同,其中Cu59团簇结构的有序程度最低.在两个Cu55团簇并合早期阶段,这两个团簇相接触后发生变形导致原子位置出现较大改变,在随后的并合过程中,原子扩散引起原子局部位置调整导致所并合体系的结构发生变化.远离两个团簇接触区的原子仍保持其并合前的结构.

Structural changes of three molten CuN （ N = 57,58,59） clusters during freezing and two Cu55 clusters with perfect icosahedral geometries in the coalescence processing at 300 K are investigated by molecular dynamics simulations based on the embedded atom method. Simulation results show that both freezing and coalescing processes have distinct stages. There exist great differences in atomic movement and microstructure change among the three CuN （N = 57,58,59） clusters during freezing, which result in the different patterns of atomic packing in the three clusters. Of the three clusters, the ordered degree of the Cu59 cluster is the lowest. Initially structural changes of the two Cu55 cluster during coalescence result from large position displacements of atoms due to the deformation, then the atomic diffusion plays a mainly role in changing structure. The atoms far from the contact region between the two clusters can remain their origin structures.