Mutual orientation of two C60 molecules: An ab initio study.

The orientational dependence of the interaction between two C₆₀ molecules is investigated using ab initio calculations. The binding energy, computed within density functional theory in the local density approximation, is substantially smaller than the one derived from the experimental heat of sublimation of fullerite, which calls into question the nature of inter-C₆₀ bonding. According to our calculations, the experimentally observed orientation with a C₆₀ presenting a hexagon-hexagon bond to a pentagonal face of the other C₆₀ is not really favored. Some other configurations are very close in energy and in fact a pentagon facing a pentagon and a hexagon facing a hexagon-hexagon bond are found to be slightly more favorable situations. Our results are compared to previous ones obtained either with previous empirical intermolecular potentials or to existing ab initio studies of crystalline C₆₀. In addition, the stacking of C₆₀ in a crystal and in a decahedral (C₆₀)₇ cluster is discussed. [ABSTRACT FROM AUTHOR]