Bloch-Redfield equations for modeling light-harvesting complexes

TL;DR

This paper defends the use of Bloch-Redfield equations for modeling exciton transport in photosynthetic complexes, emphasizing their ability to incorporate detailed physical noise effects and challenging the misconception of their limitations.

Contribution

It provides a comprehensive methodology for modeling both coherent and noisy dynamics in light-harvesting complexes using Bloch-Redfield equations, overcoming non-positivity issues and linking noise parameters to physical properties.

Findings

Bloch-Redfield approach accurately models exciton transport with physical noise considerations.

Explicit examples demonstrate modeling of coherent oscillations and noise effects.

Analysis of FMO complex shows how noise parameters influence transfer efficiency.

Abstract

We challenge the misconception that Bloch-Redfield equations are a less powerful tool than phenomenological Lindblad equations for modeling exciton transport in photosynthetic complexes. This view predominantly originates from an indiscriminate use of the secular approximation. We provide a detailed description of how to model both coherent oscillations and several types of noise, giving explicit examples. All issues with non-positivity are overcome by a consistent straightforward physical noise model. Herein also lies the strength of the Bloch-Redfield approach because it facilitates the analysis of noise-effects by linking them back to physical parameters of the noise environment. This includes temporal and spatial correlations and the strength and type of interaction between the noise and the system of interest. Finally we analyze a prototypical dimer system as well as a 7-site Fenna-Matthews-Olson (FMO) complex in regards to spatial correlation length of the noise, noise strength, temperature and their connection to the transfer time and transfer.