Exciton screening in C$_{60}$ and PTCDA complexes. TDDFT calculations with GGA and hybrid functionals
N. L. Matsko, Mahmoud A. Salem
TLDR
TDDFT calculations show hybrid functionals improve short-range exciton accuracy in C60/PTCDA, but PBE is better for long-range excitons near screening length.
Key contributions
- Studied photoabsorption in C60 and PTCDA complexes using linear response TDDFT.
- Analyzed accuracy of PBE, B3LYP, and HSE functionals for exciton energy vs. electron-hole separation.
- Hybrid functionals (B3LYP, HSE) improve accuracy for short-range excitons.
- PBE functional is more accurate than hybrids for long-range excitons near the 'screening length'.
Why it matters
This paper highlights the critical role of exchange-correlation functional choice in TDDFT for accurately modeling excitons. It shows that simpler GGA functionals can outperform hybrids for long-range charge-transfer excitons, especially near the screening length. This guides future computational studies on molecular complexes.
Original Abstract
Photoabsorption in the low-energy region for C$_{60}$ and PTCDA molecular complexes is studied within linear response TDDFT. For the PBE, B3LYP and HSE exchange-correlation (xc) functionals the dependence of the accuracy of the exciton energy on the electron-hole separation is analyzed. Particular attention is paid to the charge-transfer (CT) excitons. The inclusion of non-local exchange using hybrid functionals increases the accuracy of calculations for short-range excitons, however, the accuracy of hybrid functionals decreases significantly for long-range excitons. Moreover, as the exciton radius approaches the "screening length"\ , the simpler PBE functional gives more accurate excitonic energies than the mentioned hybrid functionals.
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