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利用密度泛函理论在B3LYP/6-31G(d)基组水平上研究了具有zigzag边界的石墨烯量子点,结果表明不同大小的石墨烯量子点的基态都是具有磁性的自旋三重态.其磁性一方面来源于zigzag边界上占有凸出位置的碳原子,另一方面来源于带有孤对电子的碳原子.从整体上看,除6b结构外,其他结构的能隙随着苯环数量的增加逐渐减小,而附加电荷却使体系能隙明显减小.用含时密度泛函理论(TD-DFT)对能隙为3.83eV的由六个苯环排列成的三角形结构进行了激发态的计算,发现第十七激发态强度最大,能量为3.93eV,对应波长315.8nm,与实验结果相近.
The graphene quantum dots with zigzag boundaries were studied at the B3LYP / 6-31G (d) basis by using density functional theory. The results show that the ground states of graphene quantum dots of different sizes are both spin-triplet magnetic states. The magnetism originates from the carbon atom which occupies the protruding position on the zigzag border and on the other hand originates from the carbon atom with the lone pair of electrons.Overall, except for the 6b structure, the energy gap of other structures increases with the benzene ring The increase of the number decreases and the additional charge decreases the energy gap of the system. The triangular structure with six benzene rings arranged by time-dependent density functional theory (TD-DFT) Excited state calculation found that the seventeenth excited state maximum intensity, energy of 3.93eV, the corresponding wavelength of 315.8nm, similar to the experimental results.