I4‾m2-C64:A novel large-cell light metallic carbon allotrope with an sp2-sp3 hybrid bonding network

A novel large-cell metallic carbon phase was proposed by combining crystal structure prediction techniques with first-principles calculations. The newly proposed metallic carbon phase belongs to a tetragonal structure (space group: I $\bar{4}$ m2), with 64 carbon atoms per unit cell. It possesses a mixture of sp² and sp³ hybridized bonds and a mass density only two-thirds that of diamond. The energy, phonon frequency, and elastic constants confirm the thermodynamical, dynamic, and mechanical stabilities of the new carbon phase, respectively. Electronic band structure calculations disclose that it exhibits metallic behavior. This novel low-density metallic carbon phase has great potential for application in electronics, aerospace, and other related fields.