Ab initio study of C9 and LaC9+ clusters

The energies and geometries of C9 and LaC9+ clusters were calculated at HF, MP2 and DFT levels. For C9, all theoretical levels show that the linear chain is the most stable structure. For LaC9+, two isomers were considered. In the first case La has two single bonds (A), while it forms a double bond in the second (B). Our results showed that in HF calculation, B is marginally more stable than A, while for MP2 and DFT, A is favored. Our results also revealed that there is not enough space for C9 ring to accomodate lanthanum. Our conclusion agrees well with experiment.