Metal-encapsulated caged clusters of germanium with large gaps and different growth behavior than silicon

Metal (M )-encapsulated caged clusters of Ge are studied using the ab initio pseudopotential plane-wave method and the generalized gradient approximation for the exchange-correlation energy. Depending upon the size of the M atom, we find Frank-Kasper polyhedral M@Ge-16 for M= Ti , Zr, Hf, and capped decahedral or cubic M@Ge-14 and M@Ge-15 clusters for several M atoms. The growth behavior differs from the one found in M@Si-n clusters. The highest-occupied-lowest-unoccupied molecular orbital gaps are, however, similarly large or even higher in some cases. Cr@Ge-16 and Fe@Ge-15 are magnetic. The weak interaction between the clusters makes such species attractive for cluster assembled materials.