Electronic and vibronic optical excitations of a quarter-filled periodic octamer

Linear optical conductivity spectra of 1-D quarter-filled charge transfer crystals are interpreted on the basis of a periodic octamer and a Holstein-Hubbard model. It is shown how the low frequency spectral features are due to combined effects of electron correlations and of the dimerization of the system. Fermion-phonon interactions introduce other spectral features which produce strong changes in the spectra.