Forces and conductances in a single-molecule bipyridine junction

TL;DR

This study uses density functional theory to analyze how contact geometry affects forces and conductance in bipyridine molecular junctions, aligning well with experimental data and highlighting the role of surface structure.

Contribution

It provides a detailed theoretical investigation of structure and electron transport in bipyridine junctions across various contact geometries, connecting computational results with experimental observations.

Findings

Force and conductance depend on surface structure.

Intermediate coordination geometries match experimental data.

Conductance is primarily mediated by the lowest unoccupied molecular orbital.

Abstract

Inspired by recent measurements of forces and conductances of bipyridine nano-junctions, we have performed density functional theory calculations of structure and electron transport in a bipyridine molecule attached between gold electrodes for seven different contact geometries. The calculations show that both the bonding force and the conductance are sensitive to the surface structure, and that both properties are in good agreement with experiment for contact geometries characterized by intermediate coordination of the metal atoms corresponding to a stepped surface. The conductance is mediated by the lowest unoccupied molecular orbital, which can be illustrated by a quantitative comparison with a one-level model. Implications for the interpretation of the experimentally determined force and conductance distributions are discussed.