Superhard polymorphs of diamond-like

Using particle swarm optimization (PSO) methodology for crystal structure prediction, we have found four potential superhard structures of P-4m2, P3m1, Pmm2 and R3m, energetically much superior to the previously proposed P-43m structure. Our density functional calculation not only confirmed these simulated structures to be superhard materials (>40 GPa), but also reveal that they exhibit metallic behavior. Further phonon and elastic constants calculations imply these structures are all mechanically stable. Therefore, they have good prospects for electronic applications as superhard materials under high pressure.