  We compare the density functional theory (DFT) results on the adsorption of
small aromatic molecules (benzene, pyridine and thiophene) on gold surfaces
obtained by using three types of van der Waals exchange-correlation functionals
and localized basis set calculations. We show that the value of the molecule
surface binding energy depends on the interplay between the BSSE effect and the
tendency of the exchange-correlation functionals to overestimate both the
molecule-surface as well as the gold-gold distances within the relaxed systems.
Consequently, we find that by using different types of LCAO basis sets or
geometric models for the adsorption of the molecules on the surface, the
binding energy can vary up to 100 %. A critical analysis of the physical
parameters resulting from the calculations is presented for each
exchange-correlation functional.
