In their initial works, Manian and co-workers noted that for perylene diimide the Herzberg-Teller contribution to internal conversion initially calculated was grossly overestimated, due in no small part to 5 high energy normal modes with nonzero Huang-Rhys factors. High energy modes have larger contributions to the Hessian, and therefore over-contribute to the rate constant. In the case of perylene diimide, two modes with significant Huang-Rhys factors of energy larger than 0.4 eV were found, corresponding to normal modes of the outermost hydrogens. Initially suggesting that this issue could be fixed through application of an alternate quantum chemical method, they argued that modes above a certain threshold energy could be truncated, yielding a rate constant of ∼10 4 s -1 . This hypothesis is bolstered when considering the molecular symmetry of ground state perylene diimide, and the fact they noted 53 transition participating normal modes for perylene diimide. Comparison of this work to work by Shi and co-workers shows the ShaMan model to perform better on the polyacenes. As well, we note that while Valiev and co-workers note the failure of the harmonic approximation in cases such as for the polyacenes, we highlight that Manian and co-workers reported fairly accurate photophysics due to the inclusion of Herzberg-Teller contributions over a Morse potential.