Methodologies are presented in which population dynamics are evolved in the exciton basis and spatiotemporal movement of excitations is subsequently obtained by projection to the site basis. Fluctuations of system eigenstates are explicitly included through vibrations of the chromophores, which are parametrized by ab initio calculations. Two limiting cases of dynamics are considered, namely, the incoherent regime, where state populations correspond to ensembles of classical Landau-Zener (LZ) trajectories, and the coherent regime, where the density matrix is propagated by the quantum Liouville equation (QLE). For QLE simulations, population dynamics show that bacteriochlorophyll a1 and a2 effectively act as a single unit at 77 K but as independent chromophores at 300 K. Population beatings for the lower energy exciton states are considerably slower at physiological temperatures, thus assisting transfer to the sink. Results from LZ trajectories indicate that, within the classical picture, higher temperatures result in a lower probability of the exciton reaching the sink. A broadening of the excitonic spectrum at high temperature alters the pathways of the excitons in the LZ formalism and also increases the possibility of trapping. This study supports the view that a coherent mechanism may assist EET at physiological temperatures since the trapping of excitations in intermediate energy sites is prevented. Furthermore, delocalized vibrations (i.e., superpositions of independent oscillators) are found to assist energy transfer at short times.
|Number of pages||10|
|Journal||Journal of Physical Chemistry B|
|Publication status||Published - 23 Feb 2015|