K6 carbon: a metallic carbon allotrope in sp3 bonding networks.

We identify by first-principles calculations a new cubic carbon phase in I4132 (O(8)) symmetry, named K6 carbon, which has a six atom primitive cell comprising sp(3) hybridized C3 triangle rings. The structural stability is verified by phonon mode analysis. The calculated elastic constants show that the K6 carbon is a high ductile material with a density even lower than graphite. Electronic band and density of states calculations reveal that it is a metallic carbon allotrope with a high electronic density of states of ∼0.10 states/eV per atom at the Fermi level. These results broaden our understanding of the structural and electronic properties of carbon allotropes.