DIMERIZATION STRUCTURES OF METALLIC AND SEMICONDUCTING FULLERENE TUBULES

Possible dimerization patterns and electronic structures in fullerene tubules considered as one-dimensional pi-conjugated systems are studied with the extended Su-Schrieffer-Heeger model. We assume various lattice geometries, including chiral and achiral tubules. The model is solved for the case of half-filled pi-electron states. (1) When the undimerized systems do not have a gap, the Kekule structures are prone to occur. The energy gap is of the order of the room temperature and metallic properties are expected to appear. (2) If the undimerized systems have a large gap (approximately 1 eV), the most stable structures are the chainlike distortions where the direction of the arranged trans-polyacetylene chains is almost along the tubular axis. The electronic structures are semiconductors due to the large gap.