【作者】 张秀梅；

【导师】 王利光；

【作者基本信息】 江南大学 ， 光学工程， 2008， 硕士

【摘要】 首先,本文研究了C₂₀三种异构体的基本结构特征,并采用HMO方法对环型,碗型,笼型三种异构体进行了稳定性比较,得到了它们的稳定性次序。然后在对C₂₀富勒烯分子了解的基础上选择了对富勒烯计算比较适合的密度泛函理论进行了所有计算。根据计算模型的需要和计算机软硬件的实际情况采用了密度泛函理论中比较常用的B3LYP方法和6-31G*基组。首先,我们对属I h对称群的C₂₀富勒烯进行了传输特性研究,然后对属于C₁对称群的C₂₀富勒烯的闭壳层基态结构为模型在高斯98上进行了结构优化,振动频率等计算,得到了属于C₁群的C₂₀富勒烯分子的能量、能级、能隙、振动光谱、电子结构等特征。它的分子轨道具有明显的离域特征,这可能是C₂₀富勒烯分子虽然违反五元环隔离规则却能够稳定存在的原因。在对C₂₀富勒烯有了更全面认识的基础上,我们又选择了迄今为止被认为是最可能稳定存在的其它几种分属D_2h, C_2h, D_3d, C₂和C_i对称群的C₂₀富勒烯进行了结构优化,频率以及NBO（自然键轨道）计算并对结果进行了分析,这也是本文的主要创新点。通过对这几种对称群C₂₀富勒烯分子的能量,能级,能隙,振动光谱以及电子结构等特征进行比较发现:最短的C-C键长为0.1368nm,最长的键长为0.1538nm,都出现在属于C 2对称群的C₂₀分子中,有明显的离域特征,与从分子轨道密度图看到的C₂₀分子的离域特征一致。分属这几种对称群的C₂₀富勒烯分子能量差别很小,能量并不随对称性降低而逐渐降低,它们基本属于等能体,并且LUMO-HOMO能隙大小也基本相同。它们的热力学稳定性顺序为: C₂> D_2h> D_3d> C_i> C_2h。分属这五种对称群的C₂₀富勒烯分子的红外光谱特征基本一致,具有数目基本相同和强度差别较小的特征峰。NBO计算表明,在这些对称群下, C₂₀分子轨道杂化特性和电荷转移特性仅存有细微的差别。从计算结果进行理论分析,振动光谱和电荷布局分析都可以作为实验上鉴定C₂₀富勒烯分子异构类型的参考。¹³ CNMR谱图是鉴别异构类型的有力工具。更多还原

【Abstract】 First, the basic structures character of the three C₂₀ isomers are studied, then the stability sequence of the three ones have been compared by the HMO method. On the basis of knowing the character of the fullerene C₂₀, the DFT theory which is suitable for the fullerene computation have been chosen to complete all the calculation. The B3LYP level and the 6-31G* basic group have been chosen when considering the real condition. The Conduction Characteristics of the C₂₀ with I h symmetry have been studied. The total energy, the energy gap, the vibration spectrum and the electronic structure character of the C₂₀ molecule with C₁ symmetry are all studied, the result suggests a pronounced degree of electron delocalization which perhaps indicates the reason of the stability of C₂₀ molecule disobeying the IPR rule. The total five possible dodecahedral structures which were computed to be the lowest-energy candidates of C₂₀ have been studied. The geometric optimization, the vibration spectrum and NBO have been computed. Those are also the innovation of the article. The results suggested that: the shortest C-C length is 0.1368nm and the longest one is 0.1538nm which all belong to the C 2 symmetry. The bond length implys the electronic delocalization which can also be seen from the DOS figures. The energies of the isomers have small difference, so do the LUMO-HOMO energy gaps of the isomers. The energies of C₂₀ does not reduce following the symmetry’s deduce. The sequence of the stability is: C₂> D_2h>D_3d>C_i>C_2h. The infrared spectrums of the five isomers are almost the same that they have almost the same number and the same intensity of the character peak value. The NBO computations suggest that the C₂₀ fullerene molecules with all those symmetry have almost the same electronic transfer characters. So theoretically speaking, the vibration spectrum and NBO results can all be the reference to differentiate the isomers. The ¹³CNMR spectrum is a strong tool to definate the isomers.更多还原