Abstract

We identify byab initiocalculations a stable three-dimensional carbon allotrope that constructed byinserting benzene rings into the carbon-carbon bonds in a previously reported oC8 carbon. This newcarbon phase has a 24-atom orthorhombic unit cell inCmmm(D192H) symmetry and thus termed oC24.Phonon mode analysis confirms its dynamical stable. Total-energy calculations show that it is energet-ically stable comparable with (5,5) carbon nanotube. Detailed electronic band calculations reveal thatoC24 is a topological node-line semimetal with two mirror-inversion symmetric nodal lines that gothrough the whole Brillouin zone in bulk and a projected surfaceflat band around the Fermi level. Thepresent results establish a new type of carbon phases and offer insights into their outstanding structuraland electronic properties.