Structure and stability of synthesized ${\mathrm{C}}_{36}$ solid [C. Piskoti, J. Yarger, and A. Zettl, Nature (London) $393,$ 771 (1998)] is investigated using a generalized tight-binding molecular-dynamics method. Out of the many solid forms considered, the most stable structure consists of a polymeric phase of ${\mathrm{C}}_{36}$ with mixed ${\mathrm{sp}}^2$ and ${\mathrm{sp}}^3$ bonding for the atoms. The cross-linking is found to be across the hexagonal faces with strong covalent intermolecular coupling. Furthermore, formation of this polymer is found to be an exothermic process. The structural properties are consistent with experiment.

• Received 11 May 1999

DOI:https://doi.org/10.1103/PhysRevB.60.13322