Reactive and Nonreactive Scattering of HCl from Au(111): An Ab Initio Molecular Dynamics Study

Abstract

The HCl + Au(111) system has recently become a benchmark for highly activated dissociative chemisorption, which presumably is strongly affected by electron–hole pair excitation. Previous dynamics calculations, which were based on density functional theory at the generalized gradient approximation level (GGA-DFT) for the molecule–surface interaction, have all overestimated measured reaction probabilities by at least an order of magnitude. Here, we perform ab initio molecular dynamics (AIMD) and AIMD with electronic friction (AIMDEF) calculations employing a density functional that includes the attractive van der Waals interaction. Our calculations model the simultaneous and possibly synergistic effects of surface temperature, surface atom motion, electron–hole pair excitation, the molecular beam conditions of the experiments, and the van der Waals interaction on the reactivity. We find that reaction probabilities computed with AIMDEF and the SRP32-vdW functional still overestimate the measured reaction probabilities, by a factor 18 for the highest incidence energy at which measurements were performed (≈2.5 eV). Even granting that the experiment could have underestimated the sticking probability by about a factor three, this still translates into a considerable overestimation of the reactivity by the current theory. Likewise, scaled transition probabilities for vibrational excitation from ν = 1, j = 1 to ν = 2 are overestimated by the AIMDEF theory, by factors 3–8 depending on the initial conditions modeled. Energy losses to the surface and translational energy losses are, however, in good agreement with experimental values.

Density Functional Theory for Molecule–Metal Surface Reactions: When Does the Generalized Gradient Approximation Get It Right, and What to Do If It Does Not

“…(Candidate SRP-DFs describe a sticking experiment on a specific system with chemical accuracy, but their validity has not (yet) been confirmed through comparison with another experiment on the same system.) However, for systems with W – E ea < 7 eV DFs with repulsive RPBE exchange either overestimate sticking notoriously 24 , 25 , 28 , 43 − 45 (red), or they show a suspect performance 26 , 27 , 29 , 46 (orange). In Figure 1 we also observe a trend that when the difference between W and E ea decreases, so that one might also expect the amount of electron transfer to increase, the SRP or GGA DF needs to be made increasingly repulsive to describe the system’s reactivity with chemical accuracy.…”

“…However, in this type of analysis evidence for strongly nonadiabatic molecule–metal surface scattering comes mostly from experiments on vibrationally inelastic scattering 51 , 52 and scattering of H atoms from metal surfaces, 53 whereas dynamics calculations only suggested small effects of electron–hole pair excitation in some of the hard to model systems in Figure 1 , i.e., D 2 O + Ni(111) 54 and HCl + Au(111). 28 More definite evidence that electronically nonadiabatic effects are most likely not the explanation for the trend observed in Figure 1 comes from a direct comparison between barrier heights obtained with first-principles and RPBE calculations. Barrier heights obtained with diffusion Monte Carlo (DMC) 55 and DFT using the RPBE and PBE DFs are compared for three H 2 + metal surface systems in Table 1 .…”

Computational approaches to dissociative chemisorption on metals: towards chemical accuracy

“…59,65,74,78,85,86,93,101,110,116,117,124,[130][131][132][133][134][135][136][137][138][139][140][141][142] However, GGAexchange DFs combined with correlation DFs approximately describing the attractive van der Waals interaction are increasingly used. 101,[143][144][145][146][147][148][149][150][151] Researchers are also starting to use meta-GGA (mGGA) DFs. 151,152 Goals of these calculations include validating models, 61,62,65,73,74,76,86,89,98,100,102,105,106,…”

“…While many studies are still performed with the Born-Oppenheimer (BO) static surface (BOSS) model, 35,43,46,48,61,65,66,76,80,82,87,88,91,98,100,103-106,110-113, 115-117,119-121,123,132,134,137,143,144,148,150-152,156,158,159,163,169,176,177,186,187 increasingly studies explicitly take into account surface atom motion 44,47,51,63,70,83-86,89,92-94,96,101,107,118,124,136,139,141,153,157,164-166, 170-173,175,181-185,188-191 or ehp excitation, 57,58,64,85,95,97,99,122,124,129,140,174 or both. 59,69,74,109,114,138,142,143,146,147,168,180,192 In some cases, ehp excitation as well as non-adiabatic electron transfer was modeled. [125][126][127][128] To give an idea of the kind of accuracy that can be achieved with standard semi-local DFs, we consider three examples that compare theory with experiment.…”

Accurate Probabilities for Highly Activated Reaction of Polyatomic Molecules on Surfaces Using a High-Dimensional Neural Network Potential: CHD3 + Cu(111)

“…2 Unfortunately, the complexity of the interaction between molecules and metals limits the accuracy of theoretical studies on these kinds of processes. 3−8 Often, chemically accurate results are obtainable at high computational cost with ab initio molecular dynamics (AIMD) combined with the so-called Specific Reaction Parameter (SRP) approach. 9−11 However, the investigation of reactions with low reactivity (<1%) remains challenging due to the need for a large number of trajectories in combination with a large computational cost.…”