New monoclinic polymorphic variety of diamond formed of graphene layers

Using the density functional theory method, geometrically optimized structure and some properties of a new carbon diamond-like phase are calculated in the local density approximation. The phase crystalline lattice is monoclinic ($P2_1/m$). This phase can be obtained by compressing the graphite in the direction of $[001]$. As a result of calculations, values of the following characteristics of the phase have been determined: the sublimation energy is $8,67$ eV/atom; the volume modulus is equal to $458$ GPa; the Vickers hardness is $90,9$ GPa; the band gap is $4,5$ eV. The calculation of graphite transformation into the monoclinic phase under compression has shown that the pressure of phase transition is $60$ GPa. The new diamond-like phase can be identified by a calculated X-ray powder diffraction pattern.