Electronic structure-factor, density matrices, and electron energy loss spectroscopy of conjugated oligomers

The electronic dynamic structure factor S(q,omega) of conjugated finite-siz e oligomers is computed using the time-dependent Hartree-Fock (TDHF) approa ch. The resonances observed in electron scattering are analyzed using the B loch representation of the single-electron transition density matrices for the corresponding polymers. The separation of relative and center-of-mass m otions of electron-hole pairs, which is expected to hold for infinite chain s, is shown to apply even for relatively small molecules, paving the way fo r a band-structure picture of the quasiparticles. Signatures of the exciton coherence sizes in the momentum dependence of the structure factor are ana lyzed.