EFFECT OF QUANTUM PHONON FLUCTUATIONS ON OPTICAL-PROPERTIES OF FINITESEMICONDUCTING CHAINS - ADIABATIC AND NONADIABATIC RESULTS

We investigate the optical properties of one-dimensional semiconductin g chains where the electron-phonon coupling represents tile dominant i nteraction. The isolated monomers possess two electronic orbitals, the lowest being occupied. In addition to hopping, two phonon modes coupl e to and mix different electronic states. We compute the optical respo nse exactly, by Lanczos algorithm, and compare it to that deduced appr oximately, within the adiabatic ansatz (i. e. factorizing the wave fun ction of the electron-phonon system). On this basis we discuss the val idity of this approximation.