Electronic structure of C and Si fullerenes and fullerides

Fullerenes, i.e., cage-structure clusters are now studied intensively as a building unit for a new class of materials. The electronic structure of C-60 and Si-20 fullerenes and their fullerides obtained in the framework of the density-functional theory is discussed with emphasis on the electronic as well as the geometrical hierarchy in superconducting fullerides. In both C-60 and Si-20 fullerides, the charge transfer from alkali atoms to fullerenes and the hybridization between alkaline-earth states and fullerene states are observed. Also A(3)C(60) and (Ba3Si3 Na@Si-20)(2) superconductors are found to have high Fermi-level density of states, although the mechanism giving it is different in two materials. Interesting materials to be produced in the future are also discussed.