Is the van der Waals interaction relevant to the dissociative dynamics of N2 on W(110)?

Abstract

Using ab initio molecular dynamics (AIMD) calculations we investigate the role of the van der Waals interaction in the dissociative adsorption of N2 on W(110). Hitherto, existing classical dynamics calculations performed on six-dimensional potential energy surfaces based on density functional theory (DFT) and semi-local exchange-correlation functionals were unable to fully describe the dependence of the initial sticking coefficient on the molecular beam incidence conditions as found in experiments. N2 dissociation on W(110) was shown to be very sensitive not only to close molecule-surface distances, but also to the large distances region where the van der Waals interaction, not included in semilocal-DFT, should dominate. In this work, we perform a systematic study on the dissociative adsorption using a selected representation of existing non-local functionals that include the van der Waals interaction. Starting with a pure static analysis of the potential energy surfaces, we find that the original vdW-DF and vdW-DF2 functionals provide a rather good description of the experimental observations regarding the adsorption well and the balance between desorption and dissociation of the chemisorbed N2. In contrast, the optimized vdW-functionals proposed in Refs. share the limitations of the (semi-local) PW91 potential energy surface for this system, i.e., an excessively deep adsorption well from which the dissociation path compared with the desorption one is energetically favored. Unexpectedly, the results of the AIMD performed at different incidence conditions are not as satisfactory as the preliminary static analysis suggested. We have to conclude that none of the used vdW-functionals seem to provide altogether an adequate description of the N2/W(110) interaction at short and large distances.