Optical excitations of Peierls–Mott insulators with bond disorder

The density-matrix renormalization group (DMRG) is employed to calculate optical properties of the half-filled Hubbard model with nearest-neighbour interactions. In order to model the optical excitations of oligoenes, a Peierls dimerization is included whose strength for the single bonds may fluctuate. Systems with up to 100 electrons are investigated, their wavefunctions are analysed, and relevant length scales for the low-lying optical excitations are identified. The approach presented provides a concise picture for the size dependence of the optical absorption in oligoenes.