The electronic structure of Ba C fullerides was studied theoretically x 60 under special consideration of electronic effects in the C molecule. Band structure 60 Ž . data were derived by an intermediate neglect of differential overlap INDO crystal Ž . orbital CO approach. Different electronic configuration were evaluated in the Ba-doped C fullerides. Ba C solids with x s 0, 3, 4, 6 are insulators. For a Ba C model 60 x 60 5 60 extrapolated from the crystal structure of Ba C , a finite band gap is also predicted. For 6 60 a Ca C -like structure of Ba C , a quasi-degeneracy between a metallic configuration 5 60 5 60 and an insulating Mott-like state was found. With an increasing Ba-to-C charge transfer 60 Ž .
CT , sizable changes in the system of C occur. In the neural molecule and for not too 60 high an electron count, the electrons form more or less electronically isolated Ž . Ž . hexagon᎐hexagon 6᎐6 ''double'' bonds with only minor hexagon᎐pentagon 6᎐5 ''double-bond'' admixtures. In the vicinity of C 12y , the 6᎐6 bonds have lost most of their 60 double-bond character while it is enhanced for the 6᎐5 bonds. In highly charged anions, the electron system of the soccer ball approaches a configuration with 12 decoupled 6 electron pentagons. For electron numbers between C and C 12y , the net bonding is 60 60 not weakened. The INDO CO results of the Ba C solids are supplemented by INDO x 60 Ž . MO and ab initio 3-21 G* split-valence basis calculations of molecular C and some 60 highly charged anions. Ab initio geometry optimizations show that the bond alternation of C with short 6᎐6 and long 6᎐5 bonds is inverted in C 12y . The high acceptor 60 60 capability of C is explained microscopically on the basis of quantum statistical 60 arguments. In the electron configurations of C and C 12y , the influence of the Pauli 60 60 Ž . Ž . antisymmetry principle PAP is minimized. The quantum statistics of electron