# Breakdown of perturbative weak coupling approaches for the biomolecular energy transfer

## TL;DR

This paper demonstrates that perturbative methods fail to accurately describe biomolecular exciton dynamics influenced by slow environmental fluctuations, highlighting the need for nonperturbative approaches in such systems.

## Contribution

The study reveals the limitations of perturbative weak coupling approaches in modeling biomolecular energy transfer under slow solvent fluctuations, emphasizing the importance of nonperturbative methods.

## Key findings

- Perturbative approaches underestimate decoherence rates by up to an order of magnitude in slow environments.
- Results agree between methods for fast environmental noise.
- Nonperturbative effects are significant in biomolecular exciton dynamics under realistic conditions.

## Abstract

We show that the biomolecular exciton dynamics under the influence of slow polarization fluctuations in the solvent cannot be described by approaches which are perturbative in the system-bath coupling. For this, we compare results for the decoherence rate of the exciton dynamics of a resumed perturbation theory with numerically exact real-time path-integral results. We find up to one order in magnitude difference in the decoherence rate for realistically slow solvent environments even in the weak coupling regime, while both results coincide for fast environmental noise. This shows explicitely the nonperturbative influence of the bioenvironmental fluctuations and might render current perturbative approaches to biomolecular exciton transport questionable.