Exciton screening in C60 and PTCDA molecular complexes and TDDFT calculations

Photoabsorption and electronic excitations in C₆₀ and PTCDA molecular complexes are studied within linear response TDDFT. For the PBE, B3LYP, HSE and HF xc functionals the dependence of the accuracy on the exciton electron-hole distance is analysed. Particular attention is paid to CT excitons with large electron-hole distances. It is shown that as the exciton radius approaches the screening length, the simpler PBE functional gives more accurate excitonic energies than the mentioned hybrid functionals.