Analysis of the non-Markovianity for electron transfer reactions in an oligothiophene-fullerene heterojunction

TL;DR

This paper investigates the non-Markovian behavior of electron transfer in an oligothiophene-fullerene heterojunction using exact hierarchical equations of motion, revealing how bath dynamics influence transfer processes and can be approximated by simpler models.

Contribution

It provides a detailed analysis of non-Markovianity in electron transfer using HEOM and compares collective bath mode effects with effective mode predictions, enhancing understanding of system-bath interactions.

Findings

Non-Markovianity varies with inter fragment distance.

The main reaction coordinate captures essential bath effects.

A simple Markovian model can approximate the dynamics under certain conditions.

Abstract

The non-Markovianity of the electron transfer in an oligothiophene-fullerene heterojunction described by a spin-boson model is analyzed using the time dependent decoherence canonical rates and the volume of accessible states in the Bloch sphere. The dynamical map of the reduced electronic system is computed by the hierarchical equations of motion methodology (HEOM) providing an exact dynamics. Transitory witness of non-Markovianity is linked to the bath dynamics analyzed from the HEOM auxiliary matrices. The signature of the collective bath mode detected from HEOM in each electronic state is compared with predictions of the effective mode extracted from the spectral density. We show that including this main reaction coordinate in a one-dimensional vibronic system coupled to a residual bath satisfactorily describes the electron transfer by a simple Markovian Redfield equation. Non-Markovianity is computed for three inter fragment distances and compared with a priori criterion based on the system and bath characteristic timescales.