Investigating of the stability and structural, mechanical and electronic properties of two new superhard conductive carbon structures

In this research, two new superhard metallic carbon allotropes αC28 and βC32 are predicted using density functional theory (DFT). These stable tetragonal structures belong to the P4/MMM space group. Molecular dynamics simulation performed under canonical ensemble (NVT) in order to investigate the thermal stability of new αC28 and βC32 carbon crystals at temperatures of 300 and 1000 K, confirms their thermal stability. In addition, we calculated mechanical coefficients and band gap energy of these two structures to examine their mechanical and electronic stability. These new carbon allotropes are composed of sp2 and sp3 bond hybridization, which shows excellent mechanical properties with Vickers hardness of 45.7 and 47.9 GPa. Other mechanical properties of these crystals such as bulk modulus (265.8, 284.9), shear modulus (254.7, 273.5) and Young's modulus (579.1, 621.6) also confirm the superhardness of these structures. The results related to the electronic band structures indicate that both structures have metallic properties. The width of both conduction and valance bands for both structures is about 20 eV. The results of calculations show that αC28 and βC32 can be synthesized in laboratory in the future and will have potential applications in mechanical and electronic devices.