Instability of tetrahedral bonding for the ${\mathrm{C}}_{100}$ molecule

The diamond-interior ${\mathrm{C}}_{100}$ molecule has been studied with a local-density-functional cluster method and found to be unstable with respect to a Jahn-Teller distortion. More seriously, the original diamondlike structure is unstable; the molecule spontaneously decomposes into an inner ${\mathrm{C}}_{20}$ core trapped iside an outer ${\mathrm{C}}_{80}$ fullerenelike shell. In essence, tetrahedral bonding throughout the molecule gives rise to 60 dangling bonds at the surface, which give way to 20 dangling bonds on the inner ${\mathrm{C}}_{20}$ surface in the double-shell fullerene. As expected, hydrogen stabilizes the tetrahedral bonding in ${\mathrm{C}}_{100}$${\mathrm{H}}_{60}$.