# Density-matrix-renormalization-group study of excitons in poly-diacetylene chains - Condensed Matter > Strongly Correlated Electrons

Abstract: We study the elementary excitations of a model Hamiltonian for the$\pi$-electrons in poly-diacetylene chains. In these materials, the bare bandgap is only half the size of the observed single-particle gap and the bindingenergy of the exciton of 0.5 eV amounts to 20% of the single-particle gap.Therefore, exchange and correlations due to the long-range Coulomb interactionrequire a numerically exact treatment which we carry out using thedensity-matrix renormalization group DMRG method. Employing both theHubbard-Ohno potential and the screened potential in one dimension, wereproduce the experimental results for the binding energy of the singletexciton and its polarizability. Our results indicate that there are opticallydark states below the singlet exciton, in agreement with experiment. Inaddition, we find a weakly bound second exciton with a binding energy of 0.1eV. The energies in the triplet sector do not match the experimental dataquantitatively, probably because we do not include polaronic relaxationeffects.

Author: Gergely Barcza, Örs Legeza, Florian Gebhard, Reinhard M. Noack

Source: https://arxiv.org/