Ab initio derivation of electronic low-energy models for C ₆₀ and aromatic compounds

We present a systematic study for understanding the relation between electronic correlation and superconductivity in C ₆₀ and aromatic compounds. We derived, from first principles, extended Hubbard models for twelve compounds: fcc K ₃C ₆₀, Rb ₃C ₆₀, Cs ₃C ₆₀ (with three different lattice constants), A15 Cs ₃C ₆₀ (with four different lattice constants), doped solid picene, coronene, and phenanthrene. We show that these compounds are strongly correlated and have similar energy scales of their bandwidths and interaction parameters. However, they have a different trend in the relation between the strength of the electronic correlation and superconducting- transition temperature. While the C ₆₀ compounds have a positive correlation, the aromatic compounds exhibit a negative correlation.