A van der Waals Inclusive Density Functional Theory Study of the Nature of Bonding for Thiophene Adsorption on Ni(100) and Cu(100) Surfaces

We report the results of the first-principles density functional theory calculations for the adsorption of thiophene (C4H4S) on Cu(100) and Ni(100) surfaces. The adsorption properties on these surfaces are evaluated for several adsorption configurations, and the calculations are performed with the inclusion of van der Waals (vdW) interactions invoking the optimized vdW (optB86b-vdW, optB88-vdW, and optPBE-vdW) as well as revPBE-vdW and rPW86-vdW2 functionals. In agreement with the earlier reports, on both surfaces, the most stable adsorption configurations correspond to the hollow-4S at which the thiophene adsorbs parallel to the surface. For the adsorption on Ni(100), in agreement with the experimental observations, we confirm that thiophene spontaneously ruptures via breaking of a C-S bond when the center of the molecule is placed over a bridge site. On the basis of both the bond distribution and charge transfer analysis, we conclude that the rupturing of thiophene observed at the bridge-45 configuration on Ni(100) may result from large charge transfer from the surface. The analyses of the electronic and geometric structures and charge transfer reveal that the interaction of the thiophene molecule with Ni(100) is much stronger than that of the Cu(100) surface. Upon adsorption of the molecule, for the former surface, we observed much larger charge transfer, non-negligible changes in the positions of the surface atoms, and appreciable electronic structure changes (i.e., in the center and width of the d-band). The adsorption of thiophene on Ni(100) also leads to the decrease in the magnetic moment of the surface Ni atoms particularly those in the vicinity of the adsorbed molecule. All these observations considered, we conclude that the nature of bonding on Ni(100) can be classified as strong chemisorption, while on Cu(100) it can be classified between weak and strong physisorption depending on the vdW functional used.