用密度泛函和遗传算法研究Cun (n≤20) 团簇的尺寸效应

结合遗传算法和Gupta多体势系统地搜索金属团簇Cu_n (n≤20)的几何结构, 并利用密度泛函方法进一步确定最稳定构型. 分析了平均键长、平均配位数、结合能、二阶差分能、电离势和电子亲和势等性质随着尺寸的变化规律. 发现在Cu₇处团簇最稳定构型从二维结构转向三维结构, Cu_n (n≤20)团簇的幻数为8, 13, 20. 团簇的键长、配位数和结合能属性随着尺寸的增长而递增最终接近相应的体相值; 而二阶差分能、电离势和电子亲和势随着尺寸增加出现奇偶交替, 说明偶数电子形成闭壳层结构, 比相邻团簇更稳定.

Study on the Size Effects of Cun (n≤20) Clusters with Combined Density Functional and Genetic Algorithm Methods

Density functional theory with plane wave basis set and genetic algorithm methods were used to investigate the structural and electronic properties of neutral copper clusters Cun with n up to 20. Properties involving the cluster size effect of average bond lengths, average coordination numbers, binding energies, second differences in total energy, ionization potentials and electron affinities were presented in detail. Changes from two dimensional to three dimensional structures were found between Cu3-6 and Cu7-20. Magic number clusters at n=8, 13 and 20 obtained from these results are in good agreement with experimental observation. The trends for the average bond lengths, average coordination numbers and binding energies almost monotonously increase with the size increment to the limits in bulk. The clear odd-even alternation for ionization potentials, electron affinities and second differences in total energy indicated the stability of electronic close shell existed in the range studied.