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First-principles study on electronic structures of graphitic compounds, BC_3 and its families

石墨化合物BC_3及其家族电子结构的第一性原理研究

基本信息

批准号：
05640372
负责人：
NAKAO Kenji
金额：
$ 1.09万
依托单位：
University of Tsukuba
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1993
资助国家：
日本
起止时间：
1993 至 1994
项目状态：
已结题

项目摘要

The recently synthesized graphitic compounds, BC_3, C_3N and BC_2N,are new layred materials and some carbon atoms in graphite, the most typycal layred material, are substituted by boron and/or nitrogen atoms. We study theoretically electronic structures of these graphitic compounds. The band structures are determined in a local-density-functional formalism using the self-consistent numerical-basis-set LCAO method.We also estimate the amount of the charge transfers among the individual atoms.The calculated band structures of graphitic compounds show that the valence bands are constituted by sigma band and pi band. These structures can be well understood based on those of the host material, graphite, but our result for BC_3 is different from that of Tomanek et al. Their band structure has a peculiar feature of the existence of pi band above the Fermi level. This may be due to the difference of the methoud of the band structure calculation.As for the charge transfer among the individual atoms, we confirm that the amounts of the charge transfer are uniquely determined by the difference of atomic energy levels of constituent atoms which corresponds to that of electronegativities of those atoms.The calculated result indicates that boron acts as a donor and nitrogen acts as an acceptor. This result also suggests that graphitic materials have the mixed bond character of the sp^2 hybridized covalent bond typical to the honeycomb network and ionic bond.We also investigate the electronic and bond structures of fullerene families and carbon nanotubes.References include some results for these studies.

最近合成的石墨化合物BC_3，C_3N和BC_2N是一类新型层状材料，其中最典型的层状材料石墨中的碳原子被硼或氮原子取代。我们从理论上研究了这些石墨化合物的电子结构。用局域密度泛函方法，采用自洽的数值基组LCAO方法，计算了石墨化合物的能带结构，并估算了原子间的电荷转移量，计算结果表明石墨化合物的价带由σ带和π带组成.这些结构可以从基质石墨的能带结构中得到很好的理解，但我们对BC_3的结果与Tomanek等人的结果不同，它们的能带结构具有费米能级以上π带存在的特殊特征。这可能是由于能带结构计算方法的不同所致.对于单个原子间的电荷转移，我们证实了电荷转移量是由组成原子的原子能级之差唯一决定的，它对应于这些原子的电负性之差.计算结果表明，硼是施主，氮是受主.这一结果也表明石墨材料具有典型的蜂窝网络sp^2杂化共价键和离子键的混合键特征。我们还研究了富勒烯家族和碳纳米管的电子和键结构。参考文献包括这些研究的一些结果。