Regensburg 2010 – scientific programme
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O: Fachverband Oberflächenphysik
O 25: Metal substrates: Adsorption of organic / bio molecules III
O 25.10: Talk
Tuesday, March 23, 2010, 12:45–13:00, H36
Nitrogen Adsorption on Graphite: Defying Physisorption — •Alexandre Tkatchenko and Matthias Scheffler — Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin, Germany
The adsorption of a nitrogen molecule at the graphite surface can be considered a paradigm
of molecular physisorption [1].
The binding of N2 can be phenomenologically described in terms of
a competition between quadrupole–quadrupole and van der Waals dispersion energies.
Of particular interest is the relative stability of the so-called “in-plane”, “out-of-plane”
and “pin-wheel” monolayer structures, in which the nitrogen molecules alternate between
parallel and perpendicular configurations on the surface.
By combining state-of-the-art electronic structure methods, such as dispersion-corrected
density-functional theory and Møller-Plesset second-order perturbation theory along with
high-level coupled cluster [CCSD(T)] calculations, we are able to gain quantitative insight
into the adsorption mechanism of N2@graphite and achieve very good agreement with experimental
desorption enthalpy. We challenge the commonly held view of a closed-shell adsorbed N2 molecule,
finding a noticeable charge-density polarization for nitrogen in a perpendicular configuration on the surface.
We map out the N2@graphite potential energy surface as a function of sliding and orientation
and discuss the influence of quantum zero-point energy for different adsorption sites.
[1] D. Marx and H. Wiechert, Adv. Chem. Phys. 95, 213 (1996).