Vibrational and Long-Range Corrections in the Reorganization Energy of Photosynthetic Molecules
Charge transport, photosynthesis
Photosynthetic organisms are responsible for the most abundant form of energy con-
version in nature. Therefore, it is important to understand how charge transport between the mo-
lecules involved in this process works. According to Marcus theory, this transport depends on
certain properties of these molecules, such as reorganization energy (λ) and Gibbs free energy.
These properties can be quantitatively estimated by applying density functional theory (DFT).
However, most pigments in photosynthesis have conjugated bonds. Thus, the alternation of
single and double bonds increases the overlap of electronic orbitals. Therefore, orbital deloca-
lization and vibrational effects are even more relevant for these molecules. Here, we calculated
the reorganization energies of 15 important molecules for photosynthesis using a reliable DFT-
based approach. The fitting of the long-range parameter of the functional reduces the effects
of orbital delocalization, while molecular vibrations are accounted for by the method of nu-
clear ensembles. The results show that the functional fitting reduces the reorganization energy,
while the vibrational effects produce distributions of this quantity, affecting charge transfer rates
between the molecules involved by up to an order of magnitude.