  The dispersion relation for noninteracting excitons and the influence of
perturbative correction is examined in the case of pentacene structure. The
values of exchange integrals are determined by the nonlinear fits to the
experimental dispersion data obtained by inelastic electron scattering in Phys.
Rev. Lett. \textbf{98}, 037402 (2007). We obtain theoretical dispersion curves
along four different directions in the Brillouin zone which possess the same
periodicity as the experimental data. We also showed that perturbative
corrections are negligible since the exciton gap in dispersion relation is huge
in comparison to exchange integrals.
