BAND-STRUCTURE STUDIES ON CRYSTALLINE C-60, CA-3, AND CA5C60

The three-dimensional EHMO crystal orbital calculations for crystalline C-60, Ca3C60, and Ca5C60 are reported. The ground states of both undoped solid C-60 and partially doped Ca3C60 are found to be insulating with an indirect energy gap of 1.2 and 0.5 eV, respectively. In contrast, Ca5C60 forms a metallic conducting phase with a set of three half-filled bands crossing the Fermi level, which is found to be located close to a peak of the density of state. The character of crystal orbitals near the Fermi level for both Ca3C60 and Ca5C60 is completely carbonlike. In both cases, the Ca atoms are almost fully ionized and C-60 molecules form a stable negative charge state with six to 10 additional electrons. (C) 1995 John Wiley & Sons, Inc.