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

We study the optical absorption spectra for various cases corresponding to halogen-bridged mixed-valent metal complexes, extending our previous calculations based on an extended Peierls-Hubbard model. Particular emphasis is placed on the changes in the spectral shapes to appear when the itineracy of electrons is increased from the localized limit. We also give special attention to the relation between the exciton band (the main band) and the photoinduced band. It is the demonstrated that, by taking account of the spectral shape of the former, we can obtain reliable information about the itineracy of electrons and determine the latter more accurately.