超长(n,n)型碳纳米管的密度泛函理论研究

用密度泛函B3LYP/3-21G(d)方法,并利用周期边界条件,研究了n=2—20不同管径的超长(n, n)型单壁碳纳米管的结构、能量、能带结构和能隙.结果表明,管径和能量(或生成焓)都随n有很好的变化规律,并可拟合成很好的解析函数.当n为2和3时,碳纳米管的能隙分别为1.836eV和0.228eV,呈半导体特征,且具有间接带隙;当n=4—20时,能隙介于0.027 eV和0.079 eV之间,呈较强的金属性,且具有直接带 关键词： 扶手椅型碳纳米管 周期边界条件(PBC) 超长模型 能带

Theoretical study on the ultra long armchair (n,n) single walled carbon nanotubes with first principle density functional theory

The armchair (n,n) single walled carbon nanotubes with n=2—20 are studied by using the first principle density functional theory at the B3LYP/3-21G(d) level of theory combined with the periodic boundary conditions in simulating the ultra long tube model. The structure parameter, the energy, the band structure, and the energy gaps are obtained. The results show that the tube diameter and the energy of formation are closely related to n. The fitted analytical equations are developed with a correlation coefficient larger than 0.999. The energy gaps of (2,2) and (3,3) carbon nanotubes are 1.836 eV and 0.228 eV and the tubes have indirect energy gaps. For n=4 to 20, the energy gaps are quite small (between 0.027 eV and 0.079 eV), showing metal conductivity as well as direct energy gaps.