title: Superhard monoclinic polymorph of carbon.
abstract: We report a novel phase of carbon possessing a monoclinic C2/m structure (8 atoms/cell) identified using an ab initio evolutionary structural search. This polymorph, which we call M-carbon, is related to the (2x1) reconstruction of the (111) surface of diamond and can also be viewed as a distorted (through sliding and buckling of the sheets) form of graphite. It is stable over cold-compressed graphite above 13.4 GPa. The simulated x-ray diffraction pattern and near K-edge spectroscopy are in satisfactory agreement with the experimental data [W. L. Mao, Science 302, 425 (2003)10.1126/science.1089713] on overcompressed graphite. The hardness and bulk modulus of this new carbon polymorph are calculated to be 83.1 and 431.2 GPa, respectively, which are comparable to those of diamond.
authors.affiliation: State Key Lab of Superhard Materials, Jilin University, Changchun 130012, China.
authors.forename: Quan
authors.initials: Q
authors.lastname: Li
authors.forename: Yanming
authors.initials: Y
authors.lastname: Ma
authors.forename: Artem R
authors.initials: AR
authors.lastname: Oganov
authors.forename: Hongbo
authors.initials: H
authors.lastname: Wang
authors.forename: Hui
authors.initials: H
authors.lastname: Wang
authors.forename: Ying
authors.initials: Y
authors.lastname: Xu
authors.forename: Tian
authors.initials: T
authors.lastname: Cui
authors.forename: Ho-Kwang
authors.initials: HK
authors.lastname: Mao
authors.forename: Guangtian
authors.initials: G
authors.lastname: Zou