Charge localisation on a redox-active single molecule junction and its influence on coherent electron transport

TL;DR

This study investigates how charge localization on a redox-active molecule affects electron transport in single-molecule junctions, using density functional theory and charge correction methods to understand complex charge transfer phenomena.

Contribution

It introduces a method to fix molecular charge in DFT calculations of electron transport, accounting for self-interaction and environmental effects in a multicomponent system.

Findings

Transmission peaks are not always pinned at the Fermi energy despite nominal charges.

Equilibrium charge transfer significantly influences electron transport properties.

Charge transfer depends on external charge and electronegativity considerations.

Abstract

For adjusting the charging state of a molecular metal complex in the context of a density functional theory description of coherent electron transport through single molecule junctions, we correct for self interaction effects by fixing the charge on a counterion, which in our calculations mimics the effect of the gate in an electrochemical STM setup, with two competing methods, namely the generalized $\Delta$ SCF technique and screening with solvation shells. One would expect a transmission peak to be pinned at the Fermi energy for a nominal charge of +1 on the molecule in the junction but we find a more complex situation in this multicomponent system defined by the complex, the leads, the counterion and the solvent. In particular equilibrium charge transfer between the molecule and the leads plays an importanty role, which we investigate in dependence on the total external charge in the context of electronegativity theory.