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

## TL;DR

This paper compares different computational methods for predicting the electronic and optical properties of two organic semiconductors, PTCDA and PDI, in both single-molecule and crystalline forms.

## Contribution

The study benchmarks GW and TDDFT methods for accuracy and cost in modeling energy and optical gaps of organic semiconductors.

## Key findings

- GW calculations are most reliable for ionization energy and electron affinity in molecular crystals.
- Single-molecule TDDFT with PCM provides good accuracy for optical gaps at lower computational cost.
- Method performance varies between single molecules and molecular crystals.

## Abstract

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.

We benchmark electronic structure methods for predicting energy and optical gaps of three organic semiconductors from molecules to crystals. GW is most reliable for crystalline energy levels, while single‐molecule time‐dependent density functional theory with a polarizable continuum model delivers remarkable accuracy for some quantities at a much lower cost. The results offer practical guidance for efficient modelling of organic semiconductors.© 2026 WILEY‐VCH GmbH