Magic Alkali-Fullerene Compound Clusters
The appearance of clusters of pronounced
stability, so-called magic clusters, is usually associated
with the formation of filled geometrical or electronic shells. For
example, the stability of C60Ba32 was explained
by the decoration of all 32 faces of a fullerene with Ba atoms ,
whereas the enhanced stability of (C60K6)nK+
was associated with the complete filling of the lowest unoccupied t1u
of C60 with the 4s1 valence electrons of K
Recently, experiments employing a different heating/cooling technique
have been performed and
a different set of magic peaks which cannot be explained by either
geometrical or electronic
shell filling arguments, has been identified .
We have used DFT to address the bonding and stability of the
experimentally observed magic clusters .
For the fullerene-potassium clusters the bonding was found to be
primarily ionic, whearas ionic and
covalent bonding were both determined to be important for those
clusters containing barium. The latter can be seen in Fig. 2 below,
which shows that the HOMO of Ba(C60)2
displays ionic bonding between the Ba 5d and C60-Π*
orbitals. Entropy was found to be vital in determining the stability of
the clusters, especially
for those containing K.
Fig. 2. The highest occupied molecular orbital (HOMO) of Ba(C60)2.
 Zimmermann, U.; Malinowski, N.; Naher, U.; Frank, S.;
Martin, T.P. Phys. Rev. Lett, 1994, 72, 3542.
 Martin, T.P.; Malinowski, N.; Zimmermann, U.; Naher, U.;
Schaber, H. J. Chem. Phys, 1993, 99, 4210.
 Enders, A.; Malinowski, N.; Ievlev, D.; Zurek, E.;
Autschbach, J.; Kern, K. J. Chem. Phys, accepted.