Dynamics of a Chlorophyll Dimer in Collective and Local Thermal Environments

TL;DR

This paper provides a comprehensive theoretical analysis of exciton transfer and decoherence in a photosynthetic dimer, incorporating collective and local environmental effects, and introduces a generalized Marcus formula applicable at various temperatures and coupling strengths.

Contribution

It introduces a generalized Marcus formula for exciton transfer rates in a dimer interacting with complex environments, valid across a wide range of parameters.

Findings

Derivation of explicit thermal relaxation and decoherence rates.

Identification of parameter regimes for the generalized Marcus formula.

Prediction of long-lived quantum coherences at ambient temperatures.

Abstract

We present a theoretical analysis of exciton transfer and decoherence effects in a photosynthetic dimer interacting with collective (correlated) and local (uncorrelated) protein-solvent environments. Our approach is based on the framework of the spin-boson model. We derive explicitly the thermal relaxation and decoherence rates of the exciton transfer process, valid for arbitrary temperatures and for arbitrary (in particular, large) interaction constants between the dimer and the environments. We establish a generalization of the Marcus formula, giving reaction rates for dimer levels possibly individually and asymmetrically coupled to environments. We identify rigorously parameter regimes for the validity of the generalized Marcus formula. The existence of long living quantum coherences at ambient temperatures emerges naturally from our approach.