Four Carbon Allotropes Form COT Structures

Abstract

On the basis of first-principles calculations, four carbon allotropes that form COT structures, c-C72, t-C80, t-C88, and c-C96 carbons, are identified in this work. The microstructures of these four carbon allotropes are highly similar, and all have a porous structure and a density lower than those of most of the reported carbon allotropes. The dynamic and mechanical stability of c-C72, t-C80, t-C88, and c-C96 carbons have been certified by elastic parameters and phonon spectra. The total energy of c-C72 carbon is only 0.163 eV/atom greater than that of diamond, and it is more energetically favorable in comparison to the previously predicted carbon structures (such as oP144, C96, C5, Pmmm C18, etc.) at zero pressure. The electronic band calculations suggest that c-C72 carbon exhibits semiconductor character with an indirect band gap of 2.27 eV, while t-C80, t-C88, and c-C96 carbons have metallic nature. Due to their lower energy and lighter weight, c-C72, t-C80, t-C88, and c-C96 carbons may possess the possibility of being applied in hydrogen storage and electronics.