Using the crystal parameters in Table , the electronic bands structures shown in Figure were obtained using the all-electrons DFT-based augmented spherical method (ASW) and the same gradient GGA XC functional . The bands develop along the main directions of the primitive tetragonal Brillouin zone. For diamond-like insulating C 4 (Fig. ), the energy level along the vertical line is with respect to the top of the valence band (VB), E V . As a specific character of diamond, the band gap of C 4 is indirect along k z between  VB and Z CB with a magnitude close to 5 eV. Oppositely, C 3 (Fig. ) is metallic-like with bands crossing the Fermi level E F . Novel C 6 (Fig. ) is identified as small gap semiconductor with the top of the valence band dominated with delocalized π electrons.