The influence of C2 dimers on the stability of Ti(m)C(n) metcar clusters.

We present results of an investigation of small Ti(m)C(n) clusters with different stoichiometries in order to throw light on the occurrence of carbon dimers in these structures. Previous studies of transition metal (M) metallocarbohedrene (metcar) clusters M(m)C(n) have proposed that C(2) dimers play a special role. In the special case of Ti(m)C(n) metcars these dimers have been observed in several studies. We shall show that clusters containing C(2) dimers are energetically favored with respect to those containing only single carbon atoms or trimers, especially when the dimers occupy the corner positions of cubic clusters. Moreover, we find that cubic structures are more stable than corresponding double-cage metcars. Finally, a highly symmetric Ti(6)C(10) metcar cluster is presented and proposed to be the global-minimum structure of this stoichiometry.