OPTICAL-ABSORPTION OF NONINTERACTING TIGHT-BINDING ELECTRONS IN A PEIERLS-DISTORTED CHAIN AT HALF BAND-FILLING

In this, the first of three articles on the optical absorption of elec trons in half-filled Peierls-distorted chains, we present analytical r esults for non-interacting tight-binding electrons. We carefully deriv e explicit expressions for the current operator, the dipole transition matrix elements and the optical absorption for electrons with a cosin e dispersion relation of bandwidth 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 f or the upper and lower Peierls subbands and the strong momentum depend ence of the transition matrix elements.