  By means of ab initio calculations within the density functional theory, we
have found that B80 fullerenes can condense to form stable face-centered-cubic
fcc solids. It is shown that when forming a crystal, B80 cages are
geometrically distorted, the Ih symmetry is lowered to Th, and four boron-boron
chemical bonds are formed between every two nearest neighbor B80 cages. The
cohesive energy of B80 fcc solid is 0.23 eV/atom with respect to the isolated
B80 fullerene. The calculated electronic structure reveals that the fcc B80
solid is a metal. The predicted solid phase would constitute a form of pure
boron and might have diverse implications. In addition, a simple electron
counting rule is proposed, which could explain the stability of B80 fullerene
and the recently predicted stable boron sheet.
