同族Ni,Pd小团簇熔化过渡异常现象

Abnormal melting transition phenomena of small Ni and Pd clusters in same group

本文运用恒温分子动力学方法及淬火技术,模型采用Gupta作用势,研究了包含相同原子数目的Ni_n和Pd_n(n=13,55,147)团簇的熔化特性.模拟结果表明:与Ni晶体熔点低于Pd晶体熔点相比,体现出团簇熔化过渡异常现象:包含相同原子数的Ni团簇的熔点高于Pd团簇的熔点.随着团簇原子数的增加,Ni团簇和Pd团簇的熔点的差值在逐渐缩小.我们研究的三个尺寸的Ni团簇的熔点的范围大致为870 K～1220 K,而Pd团簇的熔点范围大致为650 K～840 K;相应三个尺寸的Ni团簇的基态与第一激发态能量差值范围为0.65 eV～1.03 eV,Pd团簇的基态与第一激发态能量差值范围为0.38 eV～0.57 eV.具有相同原子数目的Ni团簇的基态和第一激发态能量的差值都大于Pd团簇的基态和第一激发态能量差值,我们认为这是造成这种熔化过渡异常的主要原因.

Constant - temperature molecular dynamics simulations combined with the quenching technique are used to study the melting behaviors of Ni, and Pd_n(n= 13,55,147)clusters. The Gupta form interatomic potential is adopted in the simulation. Our results show that:comparing with the lower melting point of Ni crystal than that of Pd crystal,the clusters display the abnormal melting transition phenomena :the melting point of Ni cluster is higher than that of Pd cluster,and the difference between the melting points of these two clusters decreases with increasing the cluster size. The range of melting points of the three Ni clusters is approximately 870 K～1220 K,and The range of melting points of the Pd clusters is approximately 650 K～840 K. The range of energy gap between the ground state and the first excited state of Ni clusters is 0. 65 eV～l. 03 eV,and the range of energy gap of Pd clusters is 0. 38 eV～0. 57 eV. The energy gap between the ground state and the first excited state of Ni cluster is larger than that of Pd cluster, and we think that is the main reason of such abnormal melting transition.