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

最近合成的石墨化合物BC_3、C_3N和BC_2N是一种新型层状材料，最典型的层状材料石墨中的一些碳原子被硼和/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。利用自洽数值基集LCAO方法确定了带结构的局部密度泛函形式。我们还估计了单个原子之间的电荷转移量。石墨化合物的能带结构计算表明，价带由sigma带和pi带组成。基于主体材料石墨的结构可以很好地理解这些结构，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存在π带的特点。这可能是由于带结构计算方法的不同。至于单个原子之间的电荷转移，我们确认电荷转移的数量是唯一由组成原子的原子能级的差异决定的，而原子的原子能级的差异与这些原子的电负性的差异相对应。计算结果表明，硼作为供体，氮作为受体。这一结果还表明石墨材料具有典型的蜂窝网络和离子键的sp^2杂化共价键的混合键特性。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。

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.