Nour Ghassemi

Dynamics study on dissociative chemisorption of H2 on Pt(111)

Elham Nour Ghassemi, Mark Wijzenbroek, Mark Somers and Geert-Jan Kroes

Leiden Institute of Chemistry/TC, Gorlaeus Laboratories, The Netherlands

Recently a novel implementation of the Specific Reaction Parameter (SRP) approach to Density Functional Theory (DFT) was proposed for molecule–metal surface reactions, in which the accuracy of the barrier height could be determined within chemical accuracy (1 kcal/mol ~ 4.2 kJ/mol) using density functional theory at the Generalized Gradient Approximation (GGA) level. The SRP functional was taken as a weighted average of two GGA functionals often used for the description of molecule–surface reactions. In this present work we aim to develop an SRP functional for the weakly activated H_2 + Pt(111) system. Single point DFT calculations have been performed using the Vienna ab initio Simulation Package (VASP) computer software and the corrugation reducing procedure (CRP) method has been used to interpolate the DFT results. We have studied the effects of lattice motion on the interaction of H_2 with the Pt(111) surface using a candidate SRP–DFT XC functional and investigated how the motion of surface atoms effects the dissociation barrier height and the barrier geometry. Furthermore, we present dynamics calculations on the dissociation of H_2 and D_2 on Pt(111) using the candidate SRP–DFT potential energy surface. Molecular beam simulations have been done for normal and off–normal incidence for two different incidence directions of D_2 dissociating on Pt(111) with the quasi–classical trajectory (QCT) method and diffractive scattering of H_2 from the surface has been performed with quantum dynamics using wave packets. The results are compared with available experimental data. Our dynamical calculations treat the motion of H_2 (D_2) in all six degrees of freedom. It is shown that the candidate SRP–DFT XC functional (PBE–vdW–DF) can describe reaction probabilities fairly well but fails in the description of the diffraction probabilities, not only ¬†quantitatively but also qualitatively. Our results suggest that the PBE–vdW–DF XC functional may not correctly describe the geometric corrugation of the lowest barrier.