Structural and mechanical properties of H6-carbon

First-principles density-functional investigations on H6-carbon of all sp2-bonds are presented, which show that H6-carbon is stable under isotropic deformations and tetragonal deformations of volume-conserving. However, H6-carbon cannot withstand trigonal deformations and may undergo phase transitions under triaxial shear, although it presents a bulk modulus of 273 GPa as a hard material. H6-carbon also exhibits metastability against diamond as the difference of cohesive energy is 0.80 eV. Small electronic energy gap of band structure indicates that H6-carbon is metallic.