Electronic and vibrational contributions to the reorganization energy of photosynthetic pigments

Abstract

Charge transport is dependent on properties such as reorganization energy (λ) and free energy. These quantities are typically estimated applying density functional theory (DFT) to optimized geometries. However, most pigments in photosynthesis are conjugated, making delocalization and vibrational effects relevant. Here, we calculated reorganization energies of 15 molecules relevant to photosynthesis using a reliable DFT-based approach. Tuning the functional’s long-range parameter prevents over-delocalization of orbitals, while molecular vibrations are accounted for via an ensemble method. Results show that functional tuning decreases λ, but vibrational effects produce distributions of λ, affecting charge transfer rates in up to one order of magnitude.