Computational prediction of a simple cubic carbon allotrope consisting of C 12 clusters.

We identify by ab initio calculations a new simple cubic carbon phase in Pa3¯ symmetry, which has a 48-atom unit cell in all-sp3 bonding networks, thus termed SC48 carbon. It can be viewed as a crystalline form of C12 clusters or a combined structure of SC24 and BC12 carbon, but it is energetically more stable than the recently reported cubic carbon phases such as BC8, SC24, BC12, and fcc-C12 . The structural stability is verified by phonon mode analysis. Electronic band and density of state calculations reveal that SC48 carbon is an insulator with a large direct band gap of 4.40 eV. Moreover, simulated x-ray diffraction patterns provide an excellent match to the distinct diffraction peaks found in milled fullerene soot. These results provide a solid foundation for further exploration of this new carbon allotrope.