A New Superhard -Hybridized Carbon Allotrope with Ultrawide Direct Band Gap: -C.

A novel all--hybridized superhard carbon allotrope, -C, is proposed based on first-principles calculations combined with the RG (space group and graph theory) structure search method. A systematic investigation of its stability, mechanical properties, and electronic structure is performed. The results indicate that the energy difference between -C and diamond is only 0.295 eV/atom, suggesting its metastability. Detailed analysis of its elastic constants and phonon spectrum confirms both mechanical and dynamical stability. The -C structure demonstrates exceptional mechanical performance, with a Vickers hardness of 83.9 GPa. Furthermore, it possesses a wide direct band gap of 5.58 eV, indicating that -C is a superhard semiconductor material with outstanding mechanical properties.