Superdense tI12 carbon: Unexpectedly high elastic moduli but low ideal strength

The basic physical and chemical properties of new carbon allotropies are important to explore their further technique and industrial applications. Here, a systematic theoretical investigation on the electronic, dynamical, and elastic properties for the superdense carbon (tI12) are performed, especially the ideal tensile and shear strength and the corresponding bond-breaking modes are explored to uncover its intrinsic mechanical nature and the corresponding bond-breaking modes. Our results show that the bulk, shear and Young's modulus of tI12 carbon are ultrahigh, close to those of diamond, reflecting its excellent performance of the substance's resistance to be deformed elastically at small strains. However, the calculated tensile and pure shear strengthes are remarkably lower than that of diamond, which is attributed to its original structural anisotropy by analyzing the atomic structural deformation under different strains. The current results highlighted the need to carefully examine the stress response at large strains, which provide crucial insights for the bond-breaking modes and deformation mechanisms that may lead to conclusions different from those obtained from equilibrium structures.