Ab Initio Calculation of Energy Gap and Optical Gap of Organic Semiconductors PTCDA and PDI

We applied ab initio methods, including the GW approximation, the Koopmans functionals, range-separated hybrid functionals, and time-dependent density functional theory (TDDFT) to investigate the energy gap and optical gap of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) and perylene diimide (PDI) derivatives. A detailed comparison of our calculated results from all the methods with experimental values was made, with particular focus on the properties of single molecules versus molecular crystals. Single-molecule TDDFT with the polarizable continuum model (PCM) shows reasonable accuracy for the energy and optical gaps in molecular crystals but is less accurate in predicting ionization energy (IE) and electron affinity (EA) compared to GW calculations. These findings provide guidance for selecting reliable computational approaches for evaluating key electronic and optical properties of organic semiconductor systems.