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 $M@{\mathrm{Ge}}_{16}$ for $M=\mathrm{Ti}$, Zr, Hf, and capped decahedral or cubic $M@{\mathrm{Ge}}_{14}$ and $M@{\mathrm{Ge}}_{15}$ clusters for several $M$ atoms. The growth behavior differs from the one found in $M@{\mathrm{Si}}_n$ clusters. The highest-occupied–lowest-unoccupied molecular orbital gaps are, however, similarly large or even higher in some cases. ${\mathrm{C}\mathrm{r}@\mathrm{G}\mathrm{e}}_{16}$ and ${\mathrm{F}\mathrm{e}@\mathrm{G}\mathrm{e}}_{15}$ are magnetic. The weak interaction between the clusters makes such species attractive for cluster assembled materials.

• Received 22 January 2002

DOI:https://doi.org/10.1103/PhysRevLett.88.235504