Electronic structure of Si-20 and C-20 fullerides

Recent discovery of Si-network based superconductors, Na2Ba6Si46 etc. are considered to be essentially doped solid Si-20, the dodecaheral-cage fullerene, not only geometrically but also electronically. The electronic structure obtained in the density-functional theory reveals that Ba plays an important role to give the large Fermi-level density of states and consequently, to realize the superconductivity. Although all the Si atoms are tetrahedrally coordinated, the Si-46 lattice itself is also a very interesting system having different electronic structure from that, of diamond-structure Si. The energetics as well as the electronic and structural properties of C-46 is also Studied and several interesting features have been revealed.