Influence of the van der Waals interaction in the dissociation dynamics of N2 on W(110) from first principles.

Using ab initio molecular dynamics (AIMD) calculations, we investigate the role of the van der Waals (vdW) 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 the semi-local PW91 and RPBE [Hammer et al. Phys. Rev. B 59, 7413 (1999)] 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 short molecule-surface distances but also to large distances where the vdW interaction, not included in semilocal-DFT, should dominate. In this work, we perform a systematic study on the dissociative adsorption using a selection of existing non-local functionals that include the vdW interaction (vdW-functionals). Clearly, the inclusion of the non-local correlation term contributes in all cases to correct the unrealistic energy barriers that were identified in the RPBE at large molecule-surface distances. Among the tested vdW-functionals, the original vdW-DF by Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)] and the ulterior vdW-DF2 give also an adequate description of the N2 adsorption energy and energy barrier at the transition state, i.e., of the properties that are commonly used to verify the quality of any exchange-correlation functional. However, the results of our AIMD calculations, which are performed at different incidence conditions and hence extensively probe the multi-configurational potential energy surface of the system, do not seem as satisfactory as the preliminary static analysis suggested. When comparing the obtained dissociation probabilities with existing experimental data, none of the used vdW-functionals seems to provide altogether an adequate description of the N2/W(110) interaction at short and large distances.