The role of the van der Waals interactions in the adsorption of anthracene and pentacene on the Ag(111) surface

TL;DR

This study demonstrates that incorporating van der Waals interactions in density-functional theory calculations significantly improves the accuracy of modeling anthracene and pentacene adsorption on Ag(111), affecting binding geometries and electronic properties.

Contribution

It introduces a vdW correction scheme within DFT that enhances the prediction of adsorption geometries and electronic structures for organic molecules on metal surfaces.

Findings

vdW interactions strongly influence adsorption energies and geometries

vdW corrections favor flat-lying configurations consistent with experiments

HSE-based vdW scheme improves electronic level predictions

Abstract

Using first-principles calculations based on density-functional theory (DFT) we investigated the effects of the van der Waals (vdW) interactions on the structural and electronic properties of anthracene and pentacene adsorbed on the Ag(111) surface. We found that the inclusion of vdW corrections strongly affects the binding of both anthracene/Ag(111) and pentacene/Ag(111), yielding adsorption heights and energies more consistent with the experimental results than standard DFT calculations with generalized gradient approximation (GGA). For anthracene/Ag(111) the effect of the vdW interactions is even more dramatic: we found that pure DFT-GGA calculations (without including vdW corrections) result in preference for a tilted configuration, in contrast to experimental observations of flat-lying adsorption; including vdW corrections, on the other hand, alters the binding geometry of anthracene/Ag(111), favoring the flat configuration. The electronic structure obtained using a self-consistent vdW scheme was found to be nearly indistinguishable from the conventional DFT electronic structure once the correct vdW geometry is employed for these physisorbed systems. Moreover, we show that a vdW correction scheme based on a hybrid functional DFT calculation (HSE) results in an improved description of the highest occupied molecular level of the adsorbed molecules.