The three-dimensional EHMO crystal orbital calculations for crystallin
e C-60, Ca3C60, and Ca5C60 are reported. The ground states of both und
oped 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 contra
st, Ca5C60 forms a metallic conducting phase with a set of three half-
filled bands crossing the Fermi level, which is found to be located cl
ose to a peak of the density of state. The character of crystal orbita
ls near the Fermi level for both Ca3C60 and Ca5C60 is completely carbo
nlike. In both cases, the Ca atoms are almost fully ionized and C-60 m
olecules form a stable negative charge state with six to 10 additional
electrons. (C) 1995 John Wiley & Sons, Inc.