Structural and bonding properties of bcc-based B80 solids

A density-functional-theory investigation of bcc B(80) and K(6)B(80) is presented. The calculations show that B(80) cages pack closely on a bcc lattice, with bond formation between atoms on both nearest-neighbor and next-nearest-neighbor molecules. While the binding energy of 9.9 eV/molecule is only about half that calculated for fcc B(80), potassium intercalation of bcc B(80) adds an ionic component to the binding to further stabilize the lattice. Both B(80) and K(6)B(80) are calculated to be metallic. The electronic structure is analyzed in terms of ionic and covalent effects, and the bonding is discussed in terms of a balance between two- and three-center bonding.