密度泛函理论研究EuSi_n(n=12-18)团簇的结构、稳定性与电子性质

Density-Functional Study of Structures,Relative Stabilities and Electronic Properties of EuSi_n(n=12-18) Clusters

本文采用基于密度泛函理论的B3LYP/CEP 31G方法,对EuSin(n=12-18)团簇的平衡结构、基态相对稳定性、电子性质及其随团簇尺寸的变化趋势进行了研究.结构优化和绝热电子亲和势(AEA)的计算结果表明,从n=12开始Eu原子开始占据了团簇的内部位置并形成笼状结构,同时AEA计算结果表明EuSi13团簇获得电子的能力最强.团簇的平均结合能、离解能、能量二阶差分计算结果均表明当n=13、15、17时团簇是比较稳定的.能隙分析说明Eu掺杂后团簇的化学活性有所增强,n=16时团簇具有较高化学稳定性.Mulliken布居分析表明n=13-17时电荷由Si原子向Eu原子转移而电荷转移量随n的增大而减少,在n=18时Eu原子电荷为正值开始失去电子,电荷转移方向出现了翻转.

The structures,relative stabilities and electronic properties of europium encapsulated silicon clusters [EuSin（n=12-18）] as well as the growth behavior with increasing number of Si atoms,have been investigated systematically by using B3LYP/CEP-31G method based on relativistic density-functional theory（DFT）. The optimized geometries and calculated adiabatic electron affinities（AEA） show that,for the studied clusters,Eu atoms are completely encapsulated in the Si frames and simultaneously cages form.The AEA calculations indicate also the EuSi13 cluster is more likely to obtain electron than the others.The calculations of the averaged binding energy（Eb）,the dissociation energy（ΔE）,and the second difference in energy（Δ2E） reveal that the stabilities of EuSin（n=13,15,17） clusters are larger relative to the other clusters.The calculated HOMO-LUMO energy gaps suggest that the encapsulation of Eu in the large-size silicon cluster contribute to enhancement of the chemical activity of pure silicon clusters,and the chemical stability of EuSi16 be stronger than clusters of other sizes.According to Mulliken population analysis,we find that charge always transfers from Si atom to Eu atom for EuSin（n=13-17）,with the amount decreasing as the number of Si atoms increase.However,the Eu atomic charge is positive in the EuSi18 cluster which indicates that Eu atom starts to lose electrons and the charge transfer direction of EuSin clusters reverses.