Density functional theory investigation of the structure of SO2 and SO3 on Cu(111) and Ni(111)

Density functional theory (DFT) slab calculations, mainly using the generalised gradient approximation, have been used to investigate the minimum energy structures of molecular SO2 and SO3 on Cu(111) and Ni(111) surfaces. On Ni(111) the optimal local adsorption structures are in close agreement with experimental results for both molecular species obtained using the X-ray standing wavefield technique, although for adsorbed SO2 the energetic difference between two alternative lateral positions of the lying-down molecule on the surface is marginally significant. On Cu(111) the results for adsorbed SO2, in particular, were sensitive to the DFT functional used in the calculations, but in all cases failed to reproduce the experimentally-established preference for adsorption with the molecular plane perpendicular to the surface. This result is discussed in the context of previously published DFT results for these species adsorbed on Cu(100). The optimal geometry found for SO3 on Cu(111) is similar to that on Ni(111), providing agreement with experiment regarding the molecular orientation but not the adsorption site.