The optimized ground state geometries and total energies have been determined for Ceo dimers with various structures. Neutral as well as negatively charged dimers were considered. Semiempirical calculations were performwith three different parametrizations: MNAand PM3. For the neutral and the charged dimers different structures have been found at the global energy minima. In the neutral cathe well known 66/66 cycloaddition product withD2hst symmetry was found to be the most stable configuration. In contrathe charged dimer had a different structure: it is bound through a single carbon atom on each C60ty) moiethe two balls being in trans position(C2hsymmetry). This is in accord with X-ray results on the quenched phase of A1C60(A = K,Rb). Some results of the vibrational analysis on these dimers (neutral as well as charged) are also presented in this paper.
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