Electron-phonon coupling in the one-dimensional crystals of negatively charged [18]annulene

We discuss the Jahn-Teller effect and possible superconductivity in negatively charged [18]annulene, (CH)₁₈, which is an interesting molecular system with a highly symmetric D_6h geometry in the neutral state. Electron-phonon coupling constants in model one-dimensional crystals of (CH)₁₈^-, (CH)₁₈^3-, (CD)₁₈^-, and (CD)₁₈^3- are calculated and analyzed using the B3LYP density functional method of Becke and Lee, Yang, and Parr. The lowest two frequency modes (116 cm^-1 and 405 cm^-1) causing distortions of the C-C framework of [18]annulene and the highest frequency mode (3201 cm^-1) of C-H stretching appear to give significant electron-phonon coupling constants. The computed coupling constants of the monoanion are larger than those of the trianion. Possible preconditions under which idealized one-dimensional crystals of (CH)₁₈^- and (CH)₁₈^3- can exhibit superconductivity at finite temperature are considered.