Exploring local currents in molecular junctions

Abstract

Electron transfer through molecules is an ubiquitous process underlying the function of biological systems and synthetic devices. The electronic coupling between components varies with the structure of the molecular bridge, often in classically unintuitive ways, as determined by its quantum electronic structure. Considerable efforts in electron-transfer theory have yielded models that are useful conceptually and provide quantitative means to understand transfer rates in terms of local contributions. Here we show how a description of the local currents within a bridging molecule bound to metallic electrodes can provide chemical insight into current flow. In particular, we show that through-space, as opposed to through-bond, terms dominate in a surprising number of instances, and that interference effects can be characterized by the reversal of ring currents. Together these ideas have implications for the design of molecular electronic devices, in particular for the ways in which substituent effects may be used for maximum impact.

Electronic and thermal properties of Biphenyl molecules

“…The antiresonance arises from the destructive interference between the delocalized states of the contact and the localized states in each atom when the electron cross the interface between them. This issue is in agreement with recent works in other molecular systems [19][20][21][22].…”

Atomic-Scale Control of Electron Transport through Single Molecules

“…To obtain the current pathway from molecule to surface, all local currents flowing in the bonds between individual atoms in the molecule and all atoms in the surface are summed up [24][25][26]. Since almost the entire current flow from tip to surface is via the molecule, these individual currents for each atom in the molecule add up to the total current.…”

“…The current pathway through other chemical bonds between C, N, H atoms and the surface are seen to be of minor importance. Negative bond currents are directed opposite to the total current and reflect quantum interferences, which can lead to loop currents [26].…”

A new approach to the method of source-sink potentials for molecular conduction

“…15,[60][61][62][63] In this analysis, quantisation conditions for side-chains force a node at the junction with the backbone, i.e., a CFV that kills conduction. 30 Nodal positions are robust to improvements in the level of theory if they are determined by symmetry; if they result from a cancellation within the Hückel model, they may shift, but the qualitative prediction of zero shell conduction may still be an indicator of a low contribution to conduction.…”