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Role of Long-Range Interactions for the Structure and Energetics of Olympicene Radical Adsorbed on Au(111) and Pt(111) Surfaces
journal contribution
posted on 2015-11-12, 00:00 authored by Handan Yildirim, Jeronimo Matos, Abdelkader KaraWe
report on the results of the van der Waals (vdW) inclusive density
functional theory (DFT) calculations for the adsorption characteristics
of olympicene radical (C19H11) on Au(111) and
Pt(111) surfaces. The nature of bonding between the olympicene radical
and Au(111) and Pt(111) surfaces is evaluated along with the effects
of vdW interactions, and the chemical characteristics of the surfaces,
on the adsorption. Our results show a significant increase in the
adsorption energies with the inclusion of vdW interactions, with the
largest enhancement is obtained with the optimized exchange functionals,
while a smaller enhancement is found using the rPW86-vdW2 functional,
in agreement with the trends obtained in our earlier observations
for other molecular adsorption on similar surfaces. The adsorption
of olympicene radical on Au(111) leads to negligible change in the
geometric structures of olympicene and the surface layer, while adsorption
on Pt(111) reveals significant structural changes. This observation
suggests a strong interaction with the Pt(111) surface, while the
interaction with the Au(111) surface is rather weak. While the bonding
of olympicene on Pt(111) is governed by a combination of the covalent
bonding and the vdW forces, on Au(111), the bonding is mostly governed
by the vdW forces. Upon adsorption on both surfaces, no interface
state is formed, while a charge transfer of ∼0.6 e– is obtained. We also find the surface work function to be reduced
upon adsorption on both surfaces, with the largest change observed
on Pt(111) surface, over 1 eV. On the basis of the results obtained
using the exchange functionals, we conclude that on Au(111), there
is a transition in the nature of bonding from weak physisorption to
strong physisorption, while the nature of bonding on Pt(111), is chemisorption,
and it is enhanced with the inclusion of vdWs interactions. This is
different from the adsorption on Cu(111) surface, for which we observed
a transition from weak physisorption to strong chemisorption upon
inclusion of vdW forces.