A novel allotrope of carbon with P2/m symmetry was identified during an \emph{ab-initio} minima-hopping structural search which we call M10-carbon. This structure is predicted to be more stable than graphite at pressures above 14.4 GPa and consists purely of sp3 bonds. It has a high bulk modulus and is almost as hard as diamond. A comparison of the simulated X-ray diffraction pattern shows a good agreement with experimental results from cold compressed graphite.
@article{arxiv.1202.6030,
title = {Prediction of a novel monoclinic carbon allotrope},
author = {Maximilian Amsler and José A. Flores-Livas and Silvana Botti and Miguel A. L. Marques and Stefan Goedecker},
journal= {arXiv preprint arXiv:1202.6030},
year = {2013}
}