ITINERANT MODEL VS LOCALIZED MODEL FOR MX-CHAINS - FROM THE VIEWPOINTOF THE SPECTRAL SHAPES OF OPTICAL ABSORPTIONS

We study the optical absorption spectra for various cases correspondin g to halogen-bridged mixed-valent metal complexes, extending our previ ous calculations based on an extended Peierls-Hubbard model. Particula r emphasis is placed on the changes in the spectral shapes to appear w hen the itineracy of electrons is increased from the localized limit. We also give special attention to the relation between the exciton ban d (the main band) and the photoinduced band. It is the demonstrated th at, by taking account of the spectral shape of the former, we can obta in reliable information about the itineracy of electrons and determine the latter more accurately.