Au_(85)原子纳米团簇热力学性质分子动力学模拟研究

Simulation on Thermo Dynamic Properties of Molecular Dynamics of Au_(85) Atoms Nano Clusters

采用了Johnson的(EAM)模型并结合分子动力学方法,模拟了Au_(85)原子纳米团簇熔化和凝固过程。研究了Au_(85)原子纳米团簇熔点、凝固点以及该团簇的结构,在分析势能和热容量随温度变化关系的过程中,发现Au_(85)原子纳米团簇的熔化和凝固过程中的熔点和凝固点不是线性变化,均出现了负热容现象,并且团簇的凝固点低于熔点。为了探究出现这种负热容现象的原因,对熔化过程和凝固过程中该团簇的内部结构进行了对比。结果表明,该纳米团簇在加热熔化(降温凝固)的过程中表面原子的比例显著变化,引起团簇内部势能的急剧增加(快速减少),使得动能和势能之间相互快速转化。为了维持整个系统的能量平衡,势能-温度图像发生跳变,在物理上表现为负热容现象。

Johnson＇s （EAM） model combined with molecular dynamics method was used to simulate Au85 atomic nano clusters melting and solidification process. The Au85 atomic nano clusters melting point, freezing point and structure of the cluster were researched. In the analysis of potential energy and temperature dependence of the heat capacity in the process, the change of Au85 atomic nano clusters in the melting and solidification point of melting and solidification process is not in linear. And the negative heat capacities appear, and the clusters freezing point belows the melting point. In order to explore the cause of the phenomenon of negative heat capacity, the melting process and internal structure of the atom clusters in solidification process were studied contrastively. The results show that the nano clusters on the physical structure about the ratio of the surface atoms change in the process of melting （or solidification）, which can cause the potential energy of the inner clusters rapidly increase （or reduce）, and make the rapid transformation between kinetic energy and potential energy. In order to maintain the energy balance of the system, the potential energy-temperature picture changes, which shows the phenomenon of negative heat capacity in the physical.