小尺寸铝纳米团簇的相变行为

采用分子动力学方法模拟了半径从0.3–1.3 nm变化的小尺寸铝纳米团簇的熔化、凝固行为. 基于势能-温度曲线、热容-温度曲线分析, 获得了熔点、凝固点与尺寸的依变关系, 并利用表面能理论、小尺寸效应开展了现象分析.研究表明, 铝团簇原子数小于80时, 熔点和凝固点的尺寸依赖性出现无规律的异常变化; 而大于该原子数, 熔、凝固点则随着团簇尺寸的减小而单调下降; 当原子数为27时, 团簇熔点高于块材熔点近40 K. 同时, 铝纳米团簇呈现出凝固滞后现象, 即凝固点低于熔点. 关键词： 纳米团簇 熔点 凝固点 分子动力学

Melting and freezing behavior of aluminum nanoclusters with small size

The melting and freezing behavior of small-sized aluminum nanoclusters with radii ranging from 0.3 nm to 1.3 nm are investigated by molecular dynamics simulation. Based on the potential-temperature curves and heat capacity-temperature curves, the size dependences of melting point and freezing point are obtained and the results are analysed by the surface energy theory and small size effect. The results show a non-monotonic size-dependence of the melting temperature when the atom number of nanoclusters is less than 80. For those clusters with atom number more than 80, the melting and freezing point drop down monotonically with size decreasing. For some special cases, such as aluminum nanoclusters with atom number 27, the melting point is nearly 40 K higher than the bulk melting point. Besides, we observe a rather strong hysterisis of the liquid-solid transition, which states that it is much easier for a cluster to go from ordered to disordered than for the opposite process.
Keywords： nanoclusters melting point freezing point molecular dynamics