铜团簇几何结构和结合能的半经验理论研究（Ⅲ）──平均近邻原子间距的尺寸收缩效应

Structure and Cohesive Energy of Cu Clusters(Ⅲ)──Average Atomic-distance Contraction

利用已建立的嵌入原子法描述铜团簇中原子之间的相互作用，通过优化团簇总能量，本文分别计算出一些具有立方八面体密堆结构形式的铜小团簇（原子数ｎ为１３＜ｎ＜２０１）的结构，根据本文的计算结果，团簇内部近邻原子的间距约等于大块物质的近邻原子间距ａ０，不随团簇的增大而改变；而在团簇的表层（厚约ａ０），其原子沿团簇径向有较明显的收缩；表层原子的收缩导致平均近邻原子间距的尺寸收缩效应；该平均近邻原子间距的相对收缩率在定性上约和团簇的直径成反比．同时本文比较了平均近邻原子间距收缩率的计算值和可得到的已有实验观测值．讨论了它们之间的异同。

Abstract Based on the Embedded-Atom Method, we have performed a semiempirical calculation of structure for fcc cuboctahedra copper clusters with number of atoms from 13 to 201. The corresponding average atomic-distance contractions have been derived. It is found that the distances between inner atoms are approximately equal to that or bulk metal and do not change with cluster size, while the surface atoms clearly contract along longitudinal direction, which result in the atomic-distance contraction effect. The average atomic-distance contraction is roughly inversely propotional to clusterdiameter. Our calculated results have been compared with available experimental data.