原子个数n对碳分子线C_n(n=3～10)基态结构特性的影响

The Effect of Number on the Structural Properties for Carbon Molecular Wires C_n(n=3～10) in Ground State

利用密度泛函B3LYP方法,在6-311++g**基组水平上对碳分子线Cn(n=3～10)体系的基态电子结构特性等作了理论计算.计算结果表明,当n为奇数时,碳分子线Cn基态都为单重态,反之,当n为偶数时,三重态为其稳定的基态.同时在得到碳分子线基态构型的基础上,对其极化率、电荷分布和能级分布进行了研究,确定了碳分子线体系最高占据轨道HOMO能量EH,最低未占据轨道LUMO能量EL与n的关系式,即EnH-2<EHn<EnH+2,EnL-2>ELn>EnL+2.因而碳分子线Cn(n=3～10)体系的费米能级会表现出特有的奇偶振荡,本文也对该现象出现的原因进行了讨论.

The electronic structural properties of Cn （n=3-10） molecular wires are investigated systemically using the B3LYP density functional method under the basis set 6-311＋＋g^＊＊ level. By the analysis about the calculated results, it can be found that because of the effect of delocalization, the ground state of carbon molecular wires Cn is singlet as n is odd number, whereas the triplet is the stable ground state of carbon molecular wires Cn as n is even number. Meanwhile, based on the obtained equilibrium structures in ground state, the polarizability, charge distribution and energy level distribution of carbon molecular wires have been investigated. At the same time, the relationship between high occupied molecular orbits E^H （HOMO）, low virtual molecular orbits EL （LOMO） and the number n of carbon molecular wires is determined, i. e., EH^n-2〈EH^n〈EH^n＋2,EL^n-2〉EL^n〉EL^n＋2.Therefore, the fermi levels of carbon molecular wires display their own brand of odd-even alternation properties. The reason for these properties of carbon molecular wires is explained in present work.