Optical absorption of non-interacting tight-binding electrons in a   Peierls-distorted chain at half band-filling
  In this first of three articles on the optical absorption of electrons in half-filled Peierls-distorted chains we present analytical results for non-interacting tight-binding electrons. We carefully derive explicit expressions for the current operator, the dipole transition matrix elements, and the optical absorption for electrons with a cosine dispersion relation of band width $W$ and dimerization parameter $\delta$. New correction (``$\eta$''-)terms to the current operator are identified. A broad band-to-band transition is found in the frequency range $W\delta < \omega < W$ whose shape is determined by the joint density of states for the upper and lower Peierls subbands and the strong momentum dependence of the transition matrix elements. 
F. Gebhard (ILL Grenoble, France), K. Bott, M. Scheidler, P. Thomas,   and S. W. Koch (Philipps University Marburg, Germany)