Interaction of CO with an Au monatomic chain at different strains: electronic structure and ballistic transport

TL;DR

This study investigates how CO molecules interact with gold monatomic chains under different strains, revealing the preferred adsorption sites, electronic structure details, and strain-dependent conductance changes relevant for nanoscale transport.

Contribution

It provides a detailed analysis of CO adsorption sites, electronic structure, and conductance behavior in strained gold chains, highlighting the importance of geometry and strain effects on transport properties.

Findings

Bridge site is energetically favored for CO adsorption.

Conductance is nearly zero in atop geometry due to destructive interference.

Strain affects conductance differently for atop and bridge geometries.

Abstract

We study the energetics, the electronic structure, and the ballistic transport of an infinite Au monatomic chain with an adsorbed CO molecule. We find that the bridge adsorption site is energetically favored with respect to the atop site, both at the equilibrium Au-Au spacing of the chain and at larger spacings. Instead, a substitutional configuration requires a very elongated Au-Au bond, well above the rupture distance of the pristine Au chain. The electronic structure properties can be described by the Blyholder model, which involves the formation of bonding/antibonding pairs of 5{\sigma} and 2{\pi}* states through the hybridization between molecular levels of CO and metallic states of the chain. In the atop geometry, we find an almost vanishing conductance due to the 5{\sigma} antibonding states giving rise to a Fano-like destructive interference close to the Fermi energy. In the bridge geometry, instead, the same states are shifted to higher energies and the conductance reduction with respect to pristine Au chain is much smaller. We also examine the effects of strain on the ballistic transport, finding opposite behaviors for the atop and bridge conductances. Only the bridge geometry shows a strain dependence compatible with the experimental conductance traces.