Structural and energetic parallels between hydrogenated and fluorinated fullerenes: C36X6

An exhaustive search of C36H6 and symmetrical C36F6 isomers based on the cy lindrical C-36 fullerene predicts the same D-3h structure to have the lowes t energy in each series. Some competitive structures of C36H6 have only tri vial symmetry but share the feature of 1,4 pairing of addends with the best isomer. Isostructural C36X6 (X =H, F) molecules are predicted to have cons tant energy difference. All 84 000 geometry optimisations reported here use d the DFTB model, with checking of the new parameters for CIF and F/F inter actions against LDA and GGA full density-functional methods.