Adsorption of benzene on Cu(100) and on Cu(100) covered with an ultrathin NaCl film: Molecule-substrate interaction and decoupling

We present a theoretical study of the adsorption of benzene C6H6 on the Cu(100) metal surface. The insulating effect of ionic films on this system has also been investigated by adsorbing C6H6 on the same surface covered with 1, 2, and 3 monolayers of NaCl. For this purpose, we employed density functional theory (DFT) including the van der Waals dispersion forces via a DFT-D2 scheme. For all the studied systems we analyzed the adsorption energies and geometries as well as the density of states in order to get a complete description of the type of binding, the charge transfer between the molecule and the surface, and the electronic level alignment after adsorption. We show that the molecule-substrate interaction is weak and mainly governed by dispersion forces, with an almost insignificant charge transfer between the substrate and the adsorbate. We found a progressive decoupling of the molecule from the metal surface when the size of the ultrathin insulating NaCl film increases.