富勒烯衍生物C60(CF3)n(n=2,4,6,10)几何结构和电子性质变化规律的密度泛函研究

The evolution of the structure and electronic properties of the fullerene derivatives C_(60)(CF_3)_n(n=2,4,6,10):A density functional calculation

采用密度泛函理论中的广义梯度近似对C60(CF3)n(n=2,4,6,10)几何结构和电子性质的变化规律进行了计算研究.发现在C60(CF3)4可能稳定存在的三种同分异构体中,具有p-p-p加成方式的衍生物热力学性质最为稳定;在C60(CF3)6可能稳定存在的三种同分异构体中,具有p-p-p-m-p加成方式的衍生物热力学性质最为稳定.对C60(CF3)2,C60(CF3)4,C60(CF3)6和C60(CF3)10四种加成衍生物的几何结构分析可知:随着CF3加成个数的增加,C60中的C—C平均键长逐渐变大,笼子与CF3之间连接键CC60—CCF3逐渐变大.对它们的电子结构分析可知,随着CF3加成数目的增多,反应热几乎是线性增加.而C60(CF3)n(n=2,4,6,10)分子的平均反应热在n=6处为极大值,说明C60(CF3)6应该是最容易得到的加成产物.由Mulliken电荷可知,加成的CF3个数越多,CF3与笼子的相互作用也就越强,每个CF3转移到笼子上电荷数也就越多.C60(CF3)n的自旋聚居数分布表明它们均为闭壳层结构.最后,从CF3对分子的前线轨道贡献可知,四种分子的得电子情况和失电子情况均发生在碳笼本身,并不随着CF3个数的增加而发生明显的改变.

The generalized gradient approximation（GGA）based on density functional theory（DFT）is used to analyze the evolution of the structure and electronic properties of the fullerene derivatives C60（CF3）n（n=2,4,6,10）.It is found that among the three respective possible stable isomers of C60（CF3）4 and C60（CF3）6,the structure C60（CF3）4 with p-p-p addition and C60（CF3）6 with p-p-p-m-p addition are the most stable structures,respectively.By analyzing the structures of C60（CF3）2,C60（CF3）4-1,C60（CF3）6-1,and C60（CF3）10,it was found that both the average C—C bond length and the CC60—CCF3 bond length increase with the increase of the CF3 number.It was found from the electronic properties of four compounds that the heat of reaction of the compounds almost linearly increases with the number of the CF3,and its maximum appears at n=6,thus,C60（CF3）6 should be the most easily synthesized derivative.It is known from the Mulliken charge that the interaction between CF3 and the cage and the electron transference from CF3 to the cage increase with the number of the CF3.However,the net spins of the compounds are all zero,indicative of their closed-shell electronic structures.Finally,the frontier orbital analysis shows that the electron detaching and attaching both occur at carbon sites of the cage.