CMMM-C36: a low-enthalpy sp2–sp3 hybrid carbon allotrope with one-dimensional metallicity and shear-induced self-healing

Carbon’s versatile bonding enables many allotropes; yet, combining high electrical conductivity with ultra-high mechanical strength in a single phase remains challenging. Based on a systematic CALYPSO structure search and first-principles calculations, we propose a novel sp 2 – sp 3 hybridized carbon allotrope, denoted CMMM -C 36 . It crystallizes in an orthorhombic CMMM structure and is the lowest enthalpy sp 2 – sp 3 hybrid carbon alltrope. Phonon spectra and ab initio molecular dynamics simulations confirm that CMMM -C 36 is dynamically and thermal stability at ambient conditions. Electronic-structure calculations establish that CMMM -C 36 exhibits one-dimensional metallicity. The structure also exhibits high ideal tensile and shear strength of 81–113 and 74–92 GPa, together with an unusual shear-induced damage–self-repair–strengthening response that allows shear strains exceeding 0.9 before graphitization. These features make CMMM -C 36 a promising prototype for robust carbon conductors with strongly anisotropic transport.