ROLE OF ALKALI ATOMS IN A(4)C(60)

We show that hopping via alkali atoms plays an important role for the t(1u) band of A(4)C(60) (A = K, Rb), in strong contrast to A(3)C(60) T hus the t(1u) band is broadened by more than 40% by the presence of th e alkali atoms. The difference between A(4)C(60) and A(3)C(60) is in p articular due to the less symmetric location of the alkali atoms in A( 4)C(60). We present tight-binding and ab initio band-structure calcula tions to support our conclusions.