Modelling of Oscillations in Two-Dimensional Echo-Spectra of the Fenna-Matthews-Olson Complex

TL;DR

This paper investigates the oscillations observed in two-dimensional echo-spectra of the FMO complex, demonstrating that such coherence effects persist under realistic thermal and disorder conditions using advanced numerical modeling.

Contribution

It introduces a detailed numerical approach employing hierarchical equations of motions to accurately model coherence phenomena in the FMO complex at ambient temperatures.

Findings

Oscillations in echo-spectra persist despite thermal noise.

Hierarchical equations of motions effectively model strong system-bath couplings.

Coherence effects are robust under static disorder.

Abstract

Recent experimental observations of time-dependent beatings in the two-dimensional echo-spectra of light-harvesting complexes at ambient temperatures have opened up the question whether coherence and wave-like behaviour plays a significant role in photosynthesis. We perform a numerical study of the absorption and echo-spectra of the Fenna-Matthews-Olson (FMO) complex in chlorobium tepidum and analyse the requirements in the theoretical model needed to reproduce beatings in the calculated spectra. The energy transfer in the FMO pigment-protein complex is theoretically described by an exciton Hamiltonian coupled to a phonon bath which account for the pigments electronic and vibrational excitations respectively. We use the hierarchical equations of motions method to treat the strong couplings in a non-perturbative way. We show that the oscillations in the two-dimensional echo-spectra persist in the presence of thermal noise and static disorder.