Charge transfer through molecular junctions within Redfield theory: subtleties and pitfalls

TL;DR

This paper examines the limitations of using Redfield theory to model charge transfer in molecular junctions, highlighting potential pitfalls and providing guidance on its proper application under non-equilibrium conditions.

Contribution

The study clarifies the applicability and limitations of Redfield theory for charge transfer in nanoscale junctions, especially regarding the rotating wave approximation.

Findings

Redfield theory can produce unphysical results without proper constraints.

The rotating wave approximation may not be justified under non-equilibrium conditions.

Analytical solutions illustrate the subtleties in applying the theory.

Abstract

Charge transfer through nanoscale junctions connecting metallic leads with quantum dots or single molecules is often described within an open system formulation in terms of Redfield theory. Under non-equilibrium conditions, the usually invoked rotating wave approximation is not justified which may lead to unphysical steady state solutions with e.g. negative populations. In this work we explore subtleties and constraints of the approach and thus clarify its applicability in numerical calculations. General findings are illustrated for an analytically solvable case of a molecule with two electronic states.