Abstract: Similar to the modified carbon nanotubes structure constructed by Hamada, we also constructed some simple carbon nanotubes models with the carbon element cages as the caps, which have C₅/C₃ symmetry. Under the Hückel approximation, the π electronic structures of the carbon nanotube models were calculated with the help of group reducible theorem. From these calculated results, some conclusions could be drawn: (1) For all carbon nanotube models, the average single electronic energy increases with increasing the numbers of the hexagonal layers. This implies that the longer carbon nanotubes might be potential molecules. Compared with the isolated C₅₅ and C₅₄ and the open carbon nanotubes, those models molecules are potential molecules. (2) For the molecules with subgraphs e, h and h, the number of bonding orbital is equal to that of antibonding orbital. So they are stable closed shell structure. (3) For the molecule with subgraphs a, b, c, d, f and g, the different values between the numbers of bonding and antibonding orbitals are 2,4,6,2,4 and 4, respectively. The molecules with subgraphs f also have two nonbonding orbitals. Therefore these molecules could form neutral or anion molecules. (4) The molecules with subgraphs i( k =3, 6 and 9), i'( k =1, 4, 7 and 10) and j might form cation structure as their HOMOs are nonbonding orbital. (5) The molecules with subgraphs i'( k =1, 4, 7 and 10) and j'could form cation, and those molecules with subgraphs g and d could form anion, therefore it seems that the formers could interact with the latters to form two dimensional and three-dimensional systems constructed by Hamada.

Key words: Carbon nanotubes, &pi, electronic structure, Hückel method