(AgI)_n团簇熔化行为的分子动力学模拟

Melting Behavior of (AgI)_n Clusters by Molecular Dynamics Simulation

用遗传算法结合经验势搜索了(AgI)n(n=3-15)团簇的可能稳定结构,并用微正则分子动力学方法研究了它们的熔化行为.(AgI)n团簇的稳定结构主要以四元环和六元环相接的笼状结构为主.大多数(AgI)n会在一个较大的温度范围内随温度升高结构不断扭曲,原子间距涨落及动能涨落不断增大,直到在某个温度下熔化,结构变得完全无序.(AgI)6的结构具有很高的对称性,熔化发生在一个较窄的温度范围.对于(AgI)5,会在熔化前较大的温度范围内发生最稳定结构与能量较高的环状异构体之间的转化,并可能出现负热容现象.

Lowest energy structures of （AgI）n （n=3-15） clusters were investigated by using a genetic algorithm based on empirical potential. The melting behavior of these clusters was studied by means of a microcanonical molecular dynamics simulation. Stable structures of （AgI）n clusters are mainly cages composed of four- and six-memhered rings. For most （AgI）n clusters molecular dynamics simulation shows that the fluctuation of atomic distances and kinetic energies increases with increasing temperature and the structures gradually melt within a larger temperature range. The （AgI）6 cluster has high symmetry and it melts in a narrow temperature range. For the （AgI）5 cluster the most stable cage structure may transform into a ring structure of higher energy before melting which results in negative heat capacity.