Structural and electronic properties of alpha-, beta-, gamma-, and 6,6,18-graphdiyne sheets and nanotubes

alpha-, beta-, gamma- and 6,6,18-graphdiyne (GDYs) sheets, as well as the corresponding nanotubes (GDYNTs) are investigated systematically by using the self-consistent-field crystal orbital method. The calculations show that the GDYs and GDYNTs with different structures have different electronic properties. The alpha-GDY sheet is a conductor, while 2D beta-, gamma- and 6,6,18-GDYs are semiconductors. The carrier mobilities of beta- and gamma-GDY sheets in different directions are almost the same, indicating the isotropic transport characteristics. In addition, the electron mobility is in the order of 10(6)cm(2)V(-1)s(-1)and it is two orders of magnitude larger than the hole mobility of 2D gamma-GDY. However, alpha- and 6,6,18-GDY sheets have anisotropic mobilities, which are different along different directions. For the 1D tubes, the order of stability is gamma-GDYNTs > 6,6,18-GDYNTs > beta-GDYNTs > alpha-GDYNTs and is independent of the tube chirality and size. beta- and gamma-GDYNTs as well as zigzag alpha- and 6,6,18-GDYNTs are semiconductors with direct bandgaps, while armchair alpha-GDYNTs are metals, and armchair 6,6,18-GDYNTs change from semiconductors to metals with increasing tube size. The armchair beta- and gamma-GDYNTs are more favourable to transport holes, while the corresponding zigzag tubes prefer to transport electrons.