The novel C 6 structures were derived from the orthorhombic, tetragonal, and trigonal carbon rich BC 5 by selective substitutions of boron by carbon leading to the hexacarbon systems. The structures were then geometry optimized to their respective stress-free ground states. The energy is the prevailing criterion for the first assessment of the new structures. The total energies: E total (eV) and the derived atom-averaged energies E atom are presented in Table . Additionally, the results for rh- and diamond are given. All atom-averaged values of C 6 structures are found very close to diamond, thus pointing out their stability, at least with respect to diamond.