Nonlinear network model analysis of vibrational energy transfer and localisation in the Fenna-Matthews-Olson complex

TL;DR

This study uses a nonlinear network model to analyze vibrational energy transfer and localization in the FMO complex, revealing discrete breather modes that may facilitate energy transfer and improve spectral predictions.

Contribution

The paper introduces the application of the nonlinear network model to the FMO complex, identifying discrete breather modes that influence energy transfer pathways.

Findings

Existence of nonlinear discrete breather modes in FMO

Localized modes transfer energy to core pigments

Improved agreement with experimental spectra when including localized modes

Abstract

Collective protein modes are expected to be important for facilitating energy transfer in the Fenna-Matthews-Olson (FMO) complex, however to date little work has focussed on the microscopic details of these vibrations. The nonlinear network model (NNM) provides a computationally inexpensive approach to studying vibrational modes at the microscopic level, whilst incorporating anharmonicity in the inter-residue interactions which can influence protein dynamics. We apply the NNM to the FMO complex and find evidence for the existence of nonlinear discrete breather modes. These modes tend to transfer energy to the highly connected core pigments, potentially opening up alternative excitation energy transfer routes. Incorporating localised modes based on these discrete breathers in the optical spectra calculations for FMO using ab initio site energies and excitonic couplings can substantially improve their agreement with experimental results.