Aun (n＝2～20)团簇的遗传算法和密度泛函方法研究

在遗传算法和Gupta多体势系统地搜索金属团簇初始结构基础上, 应用密度泛函理论和基于局域密度近似 (LDA)或广义梯度近似(GGA)的超软赝势和投影扩充波(PAW)方法分别系统地研究了金属团簇Au_n (n≤20)的最稳定构型和电子性质. 发现LDA或GGA近似下, 最稳定构型存在一定的差异: LDA方法中, Au团簇最稳定构型从Au₇ 处就发生了从二维结构向三维结构的转化, 而GGA近似下Au₁₃的最稳定异构体仍然保持平面构型. 计算结果表明, 平均最近邻距、平均配位数和结合能随着尺寸的增大呈递增趋势, 而二阶差分能、费米能级、HOMO-LUMO能隙、垂直电离势和电子亲和势出现了明显的奇偶交替现象. 其结果丰富了目前对金团簇的理论和实验的研究.

A Theoretical Study on Aun (n=2～20) with Combined Density Functional and Genetic Algorithm Methods

The most stable geometries and electronic properties of gold clusters Au_n (2≤n≤20) were investigated using density functional theory with ultrasoft pseudopotentials (US-PP) and projector augmented-wave (PAW) method, based on the primary structures from genetic algorithm methods. In comparison between the two sets of results based on the local density approximation (LDA) and the generalized gradient approximation (GGA), it was found that the ground state optimal geometries were planar up to n＝6 for LDA and 13 for GGA, respectively. The calculated average nearest neighbor numbers and distances, binding energies per atom almost monotonously increase to the limits in bulk. The second differences in total energy, energy gap between the highest occupied and lowest unoccupied molecular orbitals, vertical ionization potentials and electron affinities all have odd-even alternating behavior in the range studied. The results from this study enrich the recent research work for gold clusters in both theory and experiment.