Polaron Excitations in Buckminsterfullerenes: Doped C60 and C70
We propose a Su-Schrieffer-Heeger type electron-phonon model for buckminsterfullerenes: C 60 and C 70. The model is solved by a numerical iteration method with applying the adiabatic approximation to phonons. When the system ( C 60 or C 70) is doped with one or two electrons (or holes), the additional charges accumulate almost along an equatorial line of the molecule. The dimerization becomes weaker almost along the same line. Two energy levels intrude largely in the gap; one is the occupied state and the other is the empty state. The intrusion is larger in C 70 than in C 60. These are “polarons” in doped buckminsterfullerenes. It is also found that C 60 and C 70 are related mutually with respect to electronical structures as well as lattice geometries. We also calculate optical properties of C 60. In optical absorption of the doped C 60, there is a new peak at the lower energy than those of the intergap transition peaks. The third harmonic generation in low frequencies agrees with experiments. Relations of polarons with recent experiments are pointed out.