van der Waals functionals have recently been applied to obtain a potential energy surface to describe the dissociation of H2 on Ru(0001), where an improvement was found for computed reaction probabilities compared to experiment, which could not be achieved with the use of other exchange-correlation functionals. It is, however, not yet clear to what extent van der Waals functionals give a better description of other molecule-metal surface systems. In this study, the optPBE-vdW-DF functional is compared to the SRP48 functional, which was originally fitted to describe the dissociation of H2 on Cu(111), in terms of the resulting potential energy surfaces and results of quasi-classical dynamics calculations and their agreement with experiment for different H2-metal surface systems. It is found that overall the optPBE-vdW-DF functional yields potential energy surfaces that are very similar to potential energy surfaces computed with the SRP48 functional. In dynamics calculations the optPBE-vdW-DF functional gives a slightly better description of molecular beam experiments. Also a different dependence of reaction on the rotational quantum number J is found, which is in better agreement with experimental data for H2 dissociation on Cu(111). The vibrational efficacy is found to be relatively insensitive to which of the two functionals is chosen.

Static surface temperature effects on the dissociation of H 2 and D 2 on Cu(111)

Accurately describing surface temperature effects for the dissociative scattering of H2 on a metal surface on a quantum dynamical level is currently one of the open challenges for theoretical surface scientists. We present the first quantum dynamical (QD) simulations of hydrogen dissociating on a Cu(111) surface which accurately describe all relevant surface temperature effects, using the static corrugation model (SCM). The reaction probabilities we obtain show very good agreement with those found using quasi-classical dynamics (QCD), both for individual surface slabs and for an averaged, thus Monte-Carlo sampled, set of thermally distorted surface configurations. Rovibrationally elastic scattering probabilities show a much clearer difference between the QCD and QD results, which appears to be traceable back towards thermally distorted surface configurations with very low dissociation probabilities and underlines the importance of investigating more observables than just dissociation. By reducing the number of distorted surface atoms included in the dynamical model, we also show that only including one, or even three, surface atoms is generally not enough to accurately describe the effects of surface temperature on dissociation and elastic scattering. These results are a major step forward in accurately describing hydrogen scattering from a thermally excited Cu(111) surface, and open up a pathway to better describe reaction and scattering from other relevant crystal facets, such as stepped surfaces, at moderately elevated surface temperatures where quantum effects are expected to play a more important role in the dissociation of H2 on Cu.

We present results on our recently expanded static corrugation model (SCM) approach to including the relevant surface temperature effects, applied to the dissociative chemisorption reaction of H2 on a Cu(111). The reaction and rovibrationally elastic scattering probabilities we obtain at a quantum dynamical (QD) level, as an average of many statically distorted surface configurations, show great agreement with those of a dynamic surface model, which reinforces the validity of the sudden approximation inherent to the SCM. We further investigate several simple methods of binning the final rovibrational state of quasi-classical dynamics simulations, to find those best suited to reproduce QD results for our system. Finally, we show that the SCM obtained results reproduce experimental dissociation curves very well, when the uncertainty in experimental saturation values are taken into account. Some indication of a slow channel, so far only observed in experiment, can also be found at low incidence energies, although more rigorous QD simulations are required to reduce the noise inherent to our propagation methods.

State-of-the-art 6D quantum dynamics simulations for the dissociative chemisorption of H2 on a thermally distorted Cu(111) surface, using the static corrugation model, were analysed to produce several (experimentally available) observables. The expected error, especially important for lower reaction probabilities, was quantified using wavepackets on several different grids as well as two different analysis approaches to obtain more accurate results in the region where a slow reaction channel was experimentally shown to be dominant. Lowest reaction barrier sites for different thermally distorted surface slabs are shown to not just be energetically, but also geometrically, different between surface configurations, which can be used to explain several dynamical effects found when including surface temperature effects. Direct comparison of fitted time-of-flight spectra to those obtained from state-of-the-art desorption experiments showed much improved agreement compared to the perfect lattice BOSS approach. Agreement with experimental rotational and vibrational efficacies also somewhat improved when thermally excited surfaces were included in the theoretical model. Finally, we present clear quantum effects in the rotational quadrupole alignment parameters found for the lower rotationally excited states, which underlines the importance of careful quantum dynamical analyses of this system.