Properties of small carbon clusters inside the C₆₀ fullerene

We present the results of an atomic-scale simulation of the confinement of small carbon clusters inside icosahedral C₆₀ fullerene. We carefully investigate the incorporation of various clusters into C₆₀ including chains, rings, and double ring configurations, and have analyzed both the energetics and the resulting geometries. The calculations have been performed employing the density-functional-based tight-binding methodology within the self-consistent charge representation. We find that certain carbon cluster configurations that are unstable as free molecules become stabilized inside C₆₀. By adding single atoms into random positions inside the fullerene shell we establish an upper limit for the filling of C₆₀ with carbon. When the number of atoms inside the fullerene exceeds ten we observe bonding to the surrounding shell and, hence, a gradual transition of the fullerene towards an sp³ rich but locally disordered carbon system.