ISOMERS OF C-20 - DRAMATIC EFFECT OF GRADIENT CORRECTIONS IN DENSITY-FUNCTIONAL THEORY

Density functional techniques including gradient corrections are used to investigate the relative energies of the ring, bowl (corannulene-like), and cage (fullerene-like) isomers of C20. In agreement with previous studies, the local density approximation yields the cage to be the most stable isomer with the bowl and ring forms being significantly higher in energy. However, the inclusion of gradient corrections completely reverses the energy ordering of the isomers. The gradient correction alters the relative energy between the cage and ring isomers by more than 7 eV and yields the ring as the most stable form.