Jackson Koblar, Jellinek Julius
Physics Department and Science of Advanced Materials Program, Central Michigan University, Mount Pleasant, Michigan 48859, USA.
Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
J Chem Phys. 2016 Dec 28;145(24):244302. doi: 10.1063/1.4972813.
Dipole polarizabilities were computed using density functional theory for silicon clusters over a broad range of sizes up to N = 147 atoms. The calculated total effective polarizabilities, which include contributions from permanent dipole moments of the clusters, are in very good agreement with recently measured values. We show that the permanent dipole contributions are most important for clusters in the intermediate size range and that the measured polarizabilities can be used to distinguish between energetically nearly degenerate cluster isomers at these sizes. We decompose the computed total polarizabilities α into the so-called dipole and charge transfer contributions, α and α, using a site-specific analysis. When the per-atom values of these quantities are plotted against N, clear linear trends emerge that can be extrapolated to the large size limit (N→0), resulting in a value for αN of 30.5 bohrs/atom that is significantly larger than the per-atom polarizability of semiconducting bulk Si, 25.04 bohrs/atom. This indicates that Si clusters possess a higher degree of metallicity than bulk Si, a conclusion that is consistent with the strong electrostatic screening of the cluster interiors made evident by the analysis of the calculated atomic polarizabilities.
使用密度泛函理论计算了尺寸范围高达N = 147个原子的硅团簇的偶极极化率。计算得到的总有效极化率包括团簇永久偶极矩的贡献，与最近测量的值非常吻合。我们表明，永久偶极贡献对于中等尺寸范围的团簇最为重要，并且测量的极化率可用于区分这些尺寸下能量上几乎简并的团簇异构体。我们使用位点特异性分析将计算得到的总极化率α分解为所谓的偶极和电荷转移贡献α和α。当将这些量的每原子值与N作图时，会出现明显的线性趋势，可外推到较大尺寸极限（N→∞），得到αN的值为30.5玻尔/原子，明显大于半导体块状Si的每原子极化率25.04玻尔/原子。这表明硅团簇比块状Si具有更高的金属性，这一结论与通过计算原子极化率分析所表明的团簇内部的强静电屏蔽一致。
