Graphene on Ir(111): Physisorption with chemical modulation

TL;DR

This study uses advanced density functional theory to accurately model the weak van der Waals bonding of graphene on Ir(111), revealing both physisorption and localized chemical interactions.

Contribution

It demonstrates the effectiveness of the non-local vdW-DF functional in accurately predicting graphene's binding height and characterizing mixed van der Waals and chemical interactions.

Findings

Calculated graphene height matches experimental data.

Bonding is mainly van der Waals with localized covalent features.

Charge accumulation indicates weak covalent bonds.

Abstract

The non-local van der Waals density functional (vdW-DF) approach is applied to calculate the binding of graphene to Ir(111). The precise agreement of the calculated mean height h = 3.41 {\AA} of the C atoms with their mean height h = (3.38 \pm 0.04) {\AA} as measured by the X-ray standing wave (XSW) technique provides a benchmark for the applicability of the non-local functional. We find bonding of graphene to Ir(111) to be due to the van der Waals interaction with an antibonding average contribution from chemical interaction. Despite its globally repulsive character, in certain areas of the large graphene moir\'e unit cell charge accumulation between Ir substrate and grapheneC atoms is observed, signaling a weak covalent bond formation.