Accurate barriers for rate controlling elementary surface reactions are key to understanding, controlling, and predicting the rate of overall heterogeneously catalyzed processes. The specific... Show moreAccurate barriers for rate controlling elementary surface reactions are key to understanding, controlling, and predicting the rate of overall heterogeneously catalyzed processes. The specific reaction parameter approach to density functional theory (SRP-DFT) in principle allows chemically accurate barrier heights to be obtained for molecules dissociating on metal surfaces, and such accurate barriers are now available for four H2–metal and three CH4–metal systems. Also, there is some evidence that SRP density functionals (SRP-DFs) may be transferable among systems in which the same molecule interacts with a low-index face of metals belonging to the same group. To extend the SRP database, here we take a first step to obtain an SRP-DF for H2 + Ni(111) by comparing sticking probabilities (S0) computed with the quasi-classical trajectory method with S0 measured in several molecular beam experiments, using potential energy surfaces computed with several density functionals. We find that the SRP-DF for H2 + Pt(111) is not transferable to H2 + Ni(111). On the other hand, the PBE-vdW2 functional describes the molecular beam experiments on H2 + Ni(111), which we deem to be most accurate with chemical accuracy and may therefore be considered a candidate SRP-DF for this system, of which the quality still needs to be confirmed through comparison with an experiment to which it was not fitted. However, the different molecular beam sticking measurements that we considered showed discrepancies with one another and with the theory for incidence energies > 0.2 eV, and it would be good if better defined and more accurate experiments would be done for these energies to resolve these differences. Show less
It is important that theory is able to accurately describe dissociative chemisorption reactions on metal surfaces, as such reactions are often rate-controlling in heterogeneously catalyzed... Show moreIt is important that theory is able to accurately describe dissociative chemisorption reactions on metal surfaces, as such reactions are often rate-controlling in heterogeneously catalyzed processes. Chemically accurate theoretical descriptions have recently been obtained on the basis of the specific reaction parameter (SRP) approach to density functional (DF) theory (DFT), allowing reaction barriers to be obtained with chemical accuracy. However, being semiempirical, this approach suffers from two basic problems. The first is that sticking probabilities (to which SRP density functionals (DFs) are usually fitted) might show differences across experiments, of which the origins are not always clear. The second is that it has proven hard to use experiments on diffractive scattering of H2 from metals for validation purposes, as dynamics calculations using a SRP-DF may yield a rather poor description of the measured data, especially if the potential used contains a van der Waals well. We address the first problem by performing dynamics calculations on three sets of molecular beam experiments on D2 + Pt(111), using four sets of molecular beam parameters to obtain sticking probabilities, and the SRP-DF recently fitted to one set of experiments on D2 + Pt(111). It is possible to reproduce all three sets of experiments with chemical accuracy with the aid of two sets of molecular beam parameters. The theoretical simulations with the four different sets of beam parameters allow one to determine for which range of incidence conditions the experiments should agree well and for which conditions they should show specific differences. This allows one to arrive at conclusions about the quality of the experiments and about problems that might affect the experiments. Our calculations on diffraction of H2 scattering from Pt(111) show both quantitative and qualitative differences with previously measured diffraction probabilities, which were Debye–Waller (DW)-extrapolated to 0 K. We suggest that DW extrapolation, which is appropriate for direct scattering, might fail if the scattering is affected by the presence of a van der Waals well and that theory should attempt to model surface atom motion for reproducing diffraction experiments performed for surface temperatures of 500 K and higher. Show less
The accurate description of the dissociative chemisorption of a molecule on a metal surface requires a chemically accurate description of the molecule–surface interaction. Previously, it was shown... Show moreThe accurate description of the dissociative chemisorption of a molecule on a metal surface requires a chemically accurate description of the molecule–surface interaction. Previously, it was shown that the specific reaction parameter approach to density functional theory (SRP–DFT) enables accurate descriptions of the reaction of dihydrogen with metal surfaces in, for instance, H2 + Pt(111), H2 + Cu(111), and H2 + Cu(100). SRP–DFT likewise allowed a chemically accurate description of dissociation of methane on Ni(111) and Pt(111), and the SRP functional for CH4 + Ni(111) was transferable to CH4 + Pt(111), where Ni and Pt belong to the same group. Here, we investigate whether the SRP density functional derived for H2 + Cu(111) also gives chemically accurate results for H2 + Ag(111), where Ag belongs to the same group as Cu. To do this, we have performed quasi-classical trajectory calculations using the six-dimensional potential energy surface of H2 + Ag(111) within the Born–Oppenheimer static surface approximation. The computed reaction probabilities are compared with both state-resolved associative desorption and molecular beam sticking experiments. Our results do not yet show transferability, as the computed sticking probabilities and initial-state selected reaction probabilities are shifted relative to experiment to higher energies by about 2–3 kcal/mol. The lack of transferability may be due to the different character of the SRP functionals for H2 + Cu and CH4 + group 10 metals, the latter containing a van der Waals correlation functional and the former not. Show less
Using semi-empirical density functional theory and the quasi-classical trajectory (QCT) method, a specific reaction parameter (SRP) density functional is developed for the dissociation of... Show moreUsing semi-empirical density functional theory and the quasi-classical trajectory (QCT) method, a specific reaction parameter (SRP) density functional is developed for the dissociation of dihydrogen on Pt(1 1 1). The validity of the QCT method was established by showing that QCT calculations on reaction of D2 with Pt(1 1 1) closely reproduce quantum dynamics results for reaction of D2 in its rovibrational ground state. With the SRP functional, QCT calculations reproduce experimental data on D2 sticking to Pt(1 1 1) at normal and off-normal incidence with chemical accuracy. The dissociation of dihydrogen on Pt(1 1 1) is non-activated, exhibiting a minimum barrier height of −8 meV. Show less
Cueto, M. del; Muzas, A.S.; Somers, M.F.; Kroes, G.J.; Díaz, C.; Martín, F. 2017
