无限长封装过渡金属Cd的棱柱型硅纳米管的理论研究

A density functional investigation of unlimited prismy Cd encapsulated silicon nanotube atoms

运用密度泛函理论的UB3LYP/LanL2DZ方法研究了无限长封装过渡金属Cd的棱柱型硅纳米管,并讨论了它们的总能量、原子平均结合能、Mulliken原子净布局、HOMO-LUMO能隙以及电偶极距.计算结果表明无限长封装Cd的四棱柱型硅纳米管基本保持管状结构,而相应的五棱柱型则发生严重畸变.它们的最低能结构都是自旋单重态.无限长封装Cd的五棱柱型硅纳米管中所有Cd原子的Mulliken原子净布局都为正,说明电荷是从Cd原子向Si原子转移,Cd原子是电荷的施体.而有趣的是相应的四棱柱型硅纳米管里两端的Cd原子的Mulliken原子净布局为正,即Cd原子是电荷的施体,但是中间的Cd原子的的Mulliken原子净布局却为负,即电荷由Si原子向Cd原子转移,Cd原子是电荷授体,Si原子是电荷的授体,出现了电子反转.计算的HOMO-LUMO能隙说明无限长封装Cd硅纳米管中五棱柱HOMO-LUMO能隙小于四棱柱型的HOMO-LUMO能隙,说明无限长五棱柱型Cd-Si纳米管的化学活性大于相应的四棱柱型Cd-Si纳米管,且它们的HOMO-LUMO能隙均小于1.5 eV,说明它们具有半导体特性.计算的电偶极矩结果显示,无限长封装Cd的硅纳米管中,五棱柱型的硅纳米管的电偶极距为2.084 Debye,而四棱柱型的电偶极距却为零,说明无限长封装Cd的硅纳米管中四棱柱型的是非极性的,而五棱柱型的则是极性的.

The geometric structures, charge population, HOMO-LUMO gap and electric dipole moment of the unlimited quadrangular and pentagonal prism Cd encapsulated silicon nanotube are investigated computationally by density functional method at the （U）B3LYP/ LanL2DZ level. The lowest-energy structures are obtained. The results indicate that the unlimited quadrangular prism-Cd-silicon nanotube keeps the basic tube structure, but the corresponding pentagonal one is distorted seriously. The spin configurations of the lowest-energy structure for the two types of unlimited prism silicon nanotube are singlet. Meanwhile,Mulliken populations indicate that charges transfer mainly from Cd atoms to Si at- oms in the lowest-energy structure of the unlimited pentagonal prism Cd-silicon nanotube, but they transfer mainly from Si atoms to Cd which guests in the middle of the lowest-energy structure of the un- limited quadrangular prism Cd-silicon nanotube. The HOMO-LUMO gap of the unlimited quadrangular prism Cd-silicon nanotube is larger than the corresponding pentagonal one, revealing that the chemical stability of the former is larger than the latter. Also the gaps of the two type unlimited prism-Cd silicon nanotube are smaller than 1.5 eV, suggesting that they are semiconductors. The electric dipole moments of the unlimited quadrangular prism-Cd-Silicon nanotube and the corresponding pentagonal are 0 and 2. 084 Debye, respectively. This means that the former is no-polar, but the latter is polar.