A classical master equation for excitonic transport under the influence of an environment

TL;DR

This paper demonstrates that classical models can accurately replicate quantum electronic energy transfer in molecular systems, including environmental effects, challenging the notion that coherence is exclusively quantum.

Contribution

It extends previous work by incorporating environmental coupling into classical models, showing their close agreement with quantum results for EET in complex systems.

Findings

Classical models match quantum results in EET with environment coupling

Coherence in FMO complex can be explained classically

Analytical justification of classical-quantum agreement

Abstract

In a previous paper [Phys.Rev.E 83, 051911] we have shown that the results of a quantum-mechanical calculation of electronic energy transfer (EET) over aggregates of coupled monomers can be described also by a model of interacting classical electric dipoles in a weak-coupling approximation, which we referred to as the realistic coupling approximation (RCA). The method was illustrated by EET on a simple linear chain of molecules and also by energy transfer on the Fenna-Matthews-Olson (FMO) complex relevant for photosynthesis. The study was limited to electronic degrees of freedom since this is the origin of coherent EET in the quantum case. Nevertheless, more realistic models of EET require the inclusion of the de-cohering effects of coupling to an environment, when the molecular aggregate becomes an open quantum system. Here we consider the quantum description of EET on a linear chain and on the FMO complex, incorporating environment coupling and construct the classical version of the same systems in the density matrix formalism. The close agreement of the exact quantum and exact classical results in the RCA is demonstrated and justified analytically. This lends further support to the conclusion that the coherence properties of EET in the FMO complex is evident at the classical level and should not be ascribed as solely due to quantum effects.