Effects of Off-Diagonal Electron-Electron Interactions on Exciton Energies in C₆₀

Since the neighboring π orbits in C₆₀ are well overlapped, the off-diagonal part of electron interaction plays an important role. In this paper, the effects of the off-diagonal electron interactions on the exciton energies in C₆₀ are studied by using the single configuration interaction approach. It is found that the binding energies of the low-lying singlet and triplet excitons depend sensitively upon the off-diagonal interactions which compete against the diagonal interactions and suppress the binding of the excitons. The implication of these features is discussed.