Solid C-36: Crystal structures, formation, and effects of doping

We employ plane-wave pseudopotential density functional calculations to sho w that the lowest energy D-6h C-36 crystal is a highly bonded network of he xagonal planes of C-36 units with AB stacking. This crystal is significantl y more dense and lower in energy than previously proposed structures. We de monstrate that Na is the largest alkali atom that can be intercalated into the crystal structure without causing severe structural distortion. Further , we predict the reaction pathway to form a neutral C-36 dimer to be barrie rless, while negatively charged C-36 molecules are less likely to bond due to a substantial barrier of formation. [S0163-1839(99)50234-8].