Adsorption of supramolecular building blocks on graphite: a force field and density functional theory study.

The adsorption of the oligopyridine isomers 2,4’-BTP and 3,3’BTP on graphite is studied using both force-field methods and the DFT-D approach based on density functional theory together with an C6R-type dispersion correction, and the calculated adsorption energies are compared to the results of thermal desorption experiments. Whereas the used force fields yield different adsorption geometries and strongly varying adsorption energies which all overestimate the experimental value by more than 1 eV, the adsorption energy obtained in the DFT-D approach is in a rather good agreement with the experiment. This indicates that the DFT-D approach is able to reliably reproduce adsorption energies of supramolecular building blocks on graphite surfaces. Furthermore, the DFT-D calculations show that these organic molecules are almost entirely bound via the nominally weak van der Waals interaction with the strong bonding caused by the large size of the molecules.