DFT study of fullerene dimers.

Several [2+2] dimerization products of a fullerene Cn (n=50, 52, 54, 56, 58, 60) in its most stable form are presented and discussed. In total, 34 dimers are studied. Only symmetric Cn-Cn dimers (no mixed products) are reported, and only dimers of the fullerenes C50 to C58 with bonds between C atoms in adjacent pentagons are considered. Geometries were optimized within the framework of density functional theory using the Becke-Perdew exchange-correlation functional (BP86) in combination with an empirical dispersive energy correction, which contributes significantly to the binding energy. The results are discussed in the context of the reactivity of adjacent pentagon sites. The lateral interaction between fullerenes is found to be stronger for C50 to C58 than for C60, which is consistent with recent experimental observations. Further, the possibility of polymer formation based on the investigated [2+2] reaction is addressed.