Phase conversion from graphite toward a simple monoclinic sp3-carbon allotrope

We identify by ab initio calculations a simple monoclinic carbon in P2/m (C(2h)(1)) symmetry with an alternating zigzag and armchair buckling of the carbon sheets in AA stacking, which is formed via a distinct one-layer by one-layer conversion mechanism along the [210] direction assisted by a large lattice distortion. It is dynamically stable and energetically favorable as well as recently identified orthorhombic W- and monoclinic M-carbon. Moreover, this new phase has a wider band gap than diamond's, and is compatible with the experimental x-ray diffraction data. These results broaden our understanding of the direct graphite-to-diamond phase transition.