The calculated E f of C2/m is 0.203 eV/atom which is energetically more favorable than experimentally synthesized T-carbon (space group F d 3m) and other carbon allotropes such as orthorhobmic carbon oC20 78 (space group Cmcm) which have been reported. Its mechanical stability has also been validated by twelve mechanical stability criteria for orthorhombic structures. Other properties, such as mechanical properties as well as ther-mal and electronic band structure are summarized in Table and represented in Figures .