Nb_2 Si_n^+(n=1～6)团簇的密度泛函理论研究

A density functional investigation of Nb_2Si+n^+(n=1~6) clusters

运用密度泛函方法在(U)B3LYP/LanL2DZ水平上研究了Nb2Sin+(n=1～6)团簇的几何结构和电子性质.结果发现最低能Nb2Sin+团簇除了n=5,6发生了微小畸变外,其余基本保持了相应的中性Nb2Sin[(n=1～6)]团簇的结构.且除了Nb2Si+团簇外,所有的最低能结构都是自旋二重态,电子态也都为2A;由原子平均束缚能和分裂能可知,Nb2Sin+团簇的热力学稳定性比相应的Nb2Sin团簇[(n=1～6)]强,说明失去一个电子增加了团簇的热力学稳定性.且Nb2Si3+团簇的热力学稳定性是Nb2Sin+(n=1～6)团簇中最强的.从绝热电离势(AIP)和垂直电离势(VIP)的结果发现,由于VIP与AIP差值很小,说明Nb2Sin+团簇和Nb2Sin团簇[(n=1～6)]结构的构型相同.Nb2Si团簇的AIP值具有最小值6.623eV,表明在实验上很容易得到它们的阳离子形式且在质谱中可观测到较高的峰值.对HOMO-LUMO能隙的研究表明与相应的Nb2Sin(n=1～6)团簇相比,Nb2Sin+(n=1～6)团簇的HOMO-LUMO能级除了n=2,6外普遍增大,说明Nb2Sin+团簇的化学稳定性强于Nb2Sin团簇[(n=1～6)],并且除了Nb2Si3+团簇外都是半导体性的.由Mulliken电荷布局得出团簇的总磁矩和原子局域磁矩,表明Nb2Si+团簇的总磁矩最大,为3.0μB,呈现为铁磁质.硅原子则在不同的团簇中表现为顺磁性或抗磁性.

The geometric structures and electronic properties of the Nb2Si＋n（n=1~6） clusters are investigated computationally by density functional method at the（U）B3LYP/LanL2DZ level.The results indicate that the lowest-energy structure of Nb2Si＋n（n=1~6） clusters keeps the similar framework as the lowest-energy structure of the corresponding neutral clusters,except n=5 and 6.The calculated atomic averaged binding energies and fragmentation energies manifest that the thermodynamic stability of Nb2Si＋n clusters is stronger than that of the corresponding Nb2Sin clusters [（n=1~6）].The calculated vertical ionization potentials and adiabatic ionization potentials test that the structural configuration of Nb2Si＋n clusters is as same as that of Nb2Sin clusters [（n=1~6）] and the VIP of the Nb2Si cluster is the smallest,suggesting that it becomes cation most easily in the Nb2Sin（n=1~6）clusters,The HOMO-LUMO gaps manifest that the chemic stable of Nb2Si＋n（n=1~6） clusters is stronger than that of the corresponding neutral clusters and the Nb2Si＋n（n=1~6） clusters are semiconductor except Nb2Si＋3 cluster,and the total magnetic moments and the local area magnetic moments indicate that the total magnetic moment of the Nb2Si＋ cluster is largest in the Nb2Si＋n（n=1~6） clusters,and it is ferromagnetic substance,as well as test that the Nb atoms in the different clusters play different roles.