Pd_(54)团簇的熔化过程(英文)

The Melting Process of Pd_(54) Cluster

本文采用分子动力学和Gupta势函数,对一个有中心缺陷的Pd_(54)团簇的熔化性质进行了模拟研究.考虑到团簇内核原子在团簇熔化过程中起重要作用,以及无缺陷内核比有缺陷内核要稳定,由此会导致Pd_(54)团簇出现两种不同的熔化行为.本研究中,在结构转变发生时,体系总能量的增加伴随着温度的降低,这通常表明出现了负热容.但是,对于Pd_(54)团簇,这种从有中心缺陷到有表面缺陷的结构转变过程是不可逆的.正是由于该结构转变的不可逆性,使得处于平衡态下的Pd_(54)在绝大多数时间内处在有较小波动的异构体上,这种势能的较小波动表明体系动能的波动也较校由此并不会产生d_(54)团簇的负热容现象.

Using Gupta potential, we performed molecular dynamics simulation to study the melting properties of Pd54 cluster with a center vacancy. Considering the core atoms play important role in the melting process and the core atoms with a vacancy is less stable than core atoms without vacancy, the cluster will exhibit two different melting processes. In this study, increase of the total energy leads to decrease of the temperature at the structural transition stage, which generally means that the negative heat capacity occurs. But, for Pd54 cluster, there is an irreversible transition from a structure with a center vacancy to that with a vertex vacancy. Because of this irreversibility of structural transition, the system prefers to keep the structure of the isomer and has a weak fluctuation during the most time of equilibrium, and the weak fluctuation of potential energy means that the fluctuation of kinetic energy is also weak and not cause to negative heat capacity.