An MO study of neutral C8 high-symmetry clusters

Highly symmetric octacarbon clusters, i.e. a cube (Oh), a twisted cube (Td), a tricyclic cage (C3v) and a planar (D4h) structure, were fully optimized at the HF, B3LYP and MP2(Full) levels of theory. These stationary points were shown to be local minima on the potential energy surface by frequency calculations. The stability of these clusters compared to the cyclic planar (C4h) ground state was found to be strongly dependent on the level of theory. MP2(Full) calculations suggest that cubic C8 is a local minimum, its energy being 273 kJ/mol higher than the ground state. Structural parameters and fundamental vibrations are presented.