  We performed first-principles calculations aimed to investigate the role of
an heteroatom like N in the chemical and the 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 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.
