Dynamic modulation of electron correlation by intramolecular modes in charge-transfer compounds

Electron-phonon and electron-electron interactions are in competition in determining the properties of molecular charge-transfer conductors and superconductors. The direct influence of phonons on the electron-electron interaction was not before considered and in the present paper the coupling of intramolecular modes to electron-electron interaction (U-vib interaction) is investigated. The effect of this coupling on the frequency of the normal modes of a dimer model is obtained and it is shown that frequency shifts of the Raman active modes are directly related to this coupling. The results are used to obtain the values of the U-vib coupling constants of intramolecular modes of a representative molecule of charge-transfer conductors, like tetramethyl-tetratiafulvalene. Consequences of this coupling on the electron pairing are also suggested.