Chemical versus van der Waals Interaction: The Role of the Heteroatom in the Flat Absorption of Aromatic Molecules C6H6, C5NH5, and C4N2H4 on the Cu(110) Surface

We perform first-principles calculations aimed at investigating the role of a heteroatom such as N in the chemical and long-range van der Waals (vdW) interactions for a flat adsorption of several pi-conjugated molecules on the Cu(110) surface. Our study reveals that the alignment of the molecular orbitals at the adsorbate-substrate interface depends on the number of heteroatoms. As a direct consequence, the molecule-surface vdW interactions involve not only pi-like orbitals which are perpendicular to the molecular plane but also sigma-like orbitals delocalized in the molecular plane.