LAUSR

Abstract Carbon is a versatile element having many allotropes with unique properties in the periodic table. In this work, we predicted a tetragonal carbon allotrope formed by five-membered carbon cages. We studied its electronic, vibrational, dielectric, elastic, hardness and ideal strengths using first principles calculation. The results indicate that it is dynamically stable but higher in energy than graphite. It is a semiconductor having both Raman and infrared vibrational modes in its Brillouin zone center. Calculated dielectric properties reveal that it is an electronic dielectric material. It is mechanically stable but has a noticeable elastic anisotropy. Investigations of the ideal strengths indicate that c axis is more resistant against tension than a axis, but it is reversed in the case of compression. The minimum ideal strength is about 42.5/40.0 GPa occurring in the [010](100) slip system, which agrees well with the calculated hardness 41.2/39.2 GPa, so it may be a superhard material. The related fracture mechanisms at the critical strains were also discussed and illustrated by maps of electron density difference.