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The article focuses on a general discussion of scattering phenomena at condensed-phase surfaces, particularly in relation to the challenges and techniques involved in measuring angular distributions of evaporating atoms. Topics include the difficulties of measuring angular distributions from cylindrical jets versus flat jets, the prediction of helium atom evaporation patterns, and the observation of surfactant segregation in microjets.

The article focuses on a discussion about scattering in extreme environments, specifically addressing the impact of molecular orientation on nuclear spin coupling measurements. Topics include the effect of relative orientation on measurement outcomes, the role of angular momentum in molecular collisions, and the absence of significant orientation effects in the studied system.

Density functional theory (DFT) at the generalized gradient approximation (GGA) level is often considered the best compromise between feasibility and accuracy for reactions of molecules on metal surfaces. Recent work, however, strongly suggests that density functionals (DFs) based on GGA exchange are not able to describe molecule–metal surface reactions for which the work function of the metal surface minus the electron affinity of the molecule is less than 7 eV. Systems for which this is true exhibit an increased charge transfer from the metal to the molecule at the transition state, increasing the delocalisation of the electron density. This enlarged delocalisation can cause GGA-DFT to underestimate energy values relative to the gas-phase and thus underestimate the barrier height, similar to what has been observed for several gas-phase reactions. An example of such a molecule–metal surface system is O2 + Al(111). Following a similar strategy as for gas-phase reactions, previous work showed results of increased accuracy when using a screened hybrid DF for O2 + Al(111). However, even screened hybrid DFs are computationally expensive to use for metal surfaces. To resolve this, we test a non-self-consistent field (NSCF) screened hybrid DF approach. This approach computes screened hybrid DFT energies based on self-consistent-field (SCF) GGA electronic densities. Here, we explore the accuracy of the NSCF screened hybrid DF approach by implementing the NSCF HSE03-1/3x@RPBE DF for O2 + Al(111). We compute and analyse molecular beam sticking probabilities as well as a set of sticking probabilities for rotationally aligned O2. Our results show that the NSCF approach results in reaction probability curves that reproduce SCF results with near-chemical accuracy, suggesting that the NSCF approach can be used advantageously for exploratory purposes. An analysis of the potential energy surface and the barriers gives insight into the cause of the disagreement between the SCF and NSCF reaction probabilities and into the changes needed in theoretical modelling to further improve the description of the O2 + Al(111) system. Finally, the hole model yields fair agreement with dynamics results for the reaction probability curve, but results in an increased slope of the reaction probability curve compared to the molecular dynamics, with a shift to lower or higher energies depending on whether the vibrational energy of the molecule is included in the initial energy of the molecule or not. [ABSTRACT FROM AUTHOR]

Reactions of molecules on metal surfaces are notoriously difficult to simulate accurately. Density functional theory can be utilized to generate a potential energy surface, but with presently available functionals, the results are not yet accurate enough. To provide benchmark barrier heights with a high-quality method, diffusion Monte Carlo (DMC) is applied to H2 + Al(110). Barrier heights have been computed for six geometries. Our present goal is twofold: first, to provide accurate barrier heights for the two lowest lying transition states of the system, and second, to assess whether density functionals are capable of describing the variation of barrier height with molecular orientation and impact site through a comparison with DMC barriers. To this end, barrier heights computed with selected functionals at the generalized gradient approximation (GGA) and meta-GGA levels are compared to the DMC results. The comparison shows that all selected functionals yield a rather accurate description of the variation of barrier heights with impact site and orientation, although their absolute values may not be accurate. RPBE-vdW-DF and BEEF-vdW were found to perform quite well even in terms of absolute numbers. Both functionals provided barrier heights for the energetically lowest lying transition state that are within 1 kcal/mol of the DMC value. [ABSTRACT FROM AUTHOR]

Stepped transition metal surfaces, including the reconstructed Pt(110)-(2 × 1) surface, can be used to model the effect of line defects on catalysts. We present a combined experimental and theoretical study of CHD3 dissociation on this surface. Theoretical predictions for the initial sticking coefficients, S0, are obtained from ab initio molecular dynamics calculations using the specific reaction parameter (SRP) approach to density functional (DF) theory, while the measured sticking coefficients were obtained using the King and Wells method. The SRP DF used here had been previously derived for methane dissociation on Pt(111) so that the experiments test the transferability of this SRP DF to methane + Pt(110)-(2 × 1). The agreement between the experimental and calculated S0 is poor, with the average energy shift between the theoretical and measured reactivities being 20 kJ/mol. There are two factors which may contribute to this difference, the first of which is that there is a large uncertainty in the calculated sticking coefficients due to a large number of molecules being trapped on the surface at the end of the 1 ps propagation time. The second is that the SRP32-vdW functional may not accurately describe the Pt(110)-(2 × 1) surface. At the lowest incident energies considered here, Pt(110)-(2 × 1) is more reactive than the flat Pt(111) surface, but the situation is reversed at incident energies above 100 kJ/mol. [ABSTRACT FROM AUTHOR]

An important industrial process is methanol steam reforming, which is typically used in conjunction with copper catalysts. However, little agreement exists on the reaction mechanisms involved on a copper catalyst. Therefore, we have performed research yielding additional insight into the reaction mechanism for dissociative chemisorption of methanol on Cu(111) using ab initio molecular dynamics, supported by static calculations of the molecule-surface interaction with density functional theory. Our work predicts that after the initial dissociation, formaldehyde is formed through three different mechanisms. Additionally, it is observed that at high energy, CH cleavage is the dominant pathway instead of the formerly presumed OH cleavage pathway. Finally, in order to describe the interaction of methanol with the metal surface, the SRP32-vdW functional is used, which has been previously developed and tested for CHD3 on Ni(111), Pt(111), and Pt(211) using the Specific Reaction Parameter (SRP) approach. In this work, the SRP32-vdW functional is applied to methanol on Cu(111) as well, in the hope that future experiments can validate the transferability of the SRP32-vdW functional to chemically related molecule-metal surface systems. [ABSTRACT FROM AUTHOR]

The dissociation of water on a transition-metal catalyst is a fundamental step in relevant industrial processes such as the water-gas shift reaction and steam reforming. Although many theoretical studies have been performed, quantitative agreement between theoretical simulations and molecular beam experiments has not yet been achieved. In this work, we present a predictive ab initio molecular dynamics study on the dissociation of mono-deuterated water (HOD) on Ni(111). The analysis of the trajectories gives useful insight into the full-dimensional dynamics of the process and suggests that rotational steering plays a key role in the dissociation. The computed reaction probability suggests that, in combination with accurate molecular beam experiments, the specific reaction parameter density functional developed for CHD3 (SRP32-vdW) represents a good starting point for developing a semi-empirical functional able to achieve chemical accuracy for HOD on Ni(111). [ABSTRACT FROM AUTHOR]

In order to model accurately reactions of polyatomic molecules with metal surfaces important for heterogeneous catalysis in industry, the Specific Reaction Parameter (SRP) approach to density functional theory has been developed. This approach has been shown to describe the dissociation of CHD3 on Ni(111), Pt(111), and Pt(211) with chemical accuracy. In this work, predictions have been made for the reaction of CHD3 on Cu(111) and Cu(211) using barriers, elbow plots, and ab initio molecular dynamics. Future experiments could hopefully prove the transferability of the SRP functional to systems in which methane reacts with flat and stepped surfaces of adjacent groups of the periodic table, by comparison with our predictions. Moreover, the effect of a so-called single atom alloy on the reactivity of methane is investigated by making predictions for CHD3 on Pt–Cu(111) and Pd–Cu(111). It is found that the reactivity is only increased for Pt–Cu(111) near the alloyed atom, which is not only caused by the lowering of the barrier height but also by changes in the dynamical pathway and reduction of energy transfer from methane to the surface. [ABSTRACT FROM AUTHOR]

The simulation of the dissociation of molecules on metal surfaces is a cornerstone for the understanding of heterogeneously catalyzed processes. However, due to high computational demand, the accurate dynamical simulation of the dissociative chemisorption of polyatomic molecules has been limited mostly to flat low-index metal surfaces. The study of surfaces that feature "defected" sites, such as steps, is crucial to improve the understanding of the overall catalytic process due to the high reactivity of under-coordinated sites for this kind of reaction. In this work, we have extensively analyzed more than 10 000 ab initio molecular dynamics trajectories where a CHD3 molecule is impinging either on the flat Pt(111) surface or on the stepped Pt(211) surface for different initial rovibrational states and collision energies. The results have been compared in order to get insight into the effect of the step in the dissociation of methane. We have found that, despite a large difference in the activation barrier and consequently in reactivity, the geometry of the lowest transition states is very similar on the two surfaces and this results in a similar dissociation dynamics. Furthermore, the trapping observed on the Pt(211) surface can be explained with energy transfer to parallel translational motion induced by the geometry of the slab and by a larger energy transfer to phonons for the stepped Pt(211) surface. [ABSTRACT FROM AUTHOR]

The application of orbital-free density functional theory (OF-DFT) to NaAlH4, a potential hydrogen storage material, and related systems is presented. Calculations on AlH3 show that the failure to describe the Al-H interaction is related to the kinetic energy, functionals used rather than the local pseudopotentials, which are required within the OF-DFT approach.

The dissociative chemisorption of hydrogen on metal surfaces is examined in the light of quantum mechanics using density functional theory for interpreting molecule-surface interaction and quantum dynamics for simulating hydrogen atom motion.

In this work, we explore the suitability of several density functionals with the generalized gradient approximation (GGA) and beyond for describing the dissociative chemisorption of methane on the reconstructed Pt(110)-(2×1) surface. The bulk and surface structures of the metal, methane adsorption energy, and dissociation barrier are used to assess the functionals. A van der Waals corrected GGA functional (optPBE-vdW) and a meta-GGA functional with van der Waals correction (MS PBEl-rVV10) are selected for ab initio molecular dynamics calculations of the sticking probability. Our results suggest that the use of these two functionals may lead to a better agreement with existing experimental results, thus serving as a good starting point for future development of reliable machine-learned potential energy surfaces for the dissociation of methane on the Pt(110)-(2×1) surface. [ABSTRACT FROM AUTHOR]

We have performed calculations on the dissociative chemisorption of H2 on un-reconstructed and reconstructed Au(111) with density functional theory, and dynamics calculations on this process on un-reconstructed Au(111). Due to a very late barrier for dissociation, H2 + Au(111) is a candidate H2-metal system for which the dissociative chemisorption could be considerably affected by the energy transfer to electron-hole pairs. Minimum barrier geometries and potential energy surfaces were computed for six density functionals. The functionals tested yield minimum barrier heights in the range of 1.15-1.6 eV, and barriers that are even later than found for the similar H2 + Cu(111) system. The potential energy surfaces have been used in quasi-classical trajectory calculations of the initial (v,J) state resolved reaction probability for several vibrational states v and rotational states J of H2 and D2. Our calculations may serve as predictions for state-resolved associative desorption experiments, from which initial state-resolved dissociative chemisorption probabilities can be extracted by invoking detailed balance. The vibrational efficacy ηv=0→1 reported for D2 dissociating on un-reconstructed Au(111) (about 0.9) is similar to that found in earlier quantum dynamics calculations on H2 + Ag(111), but larger than found for D2 + Cu(111). With the two functionals tested most extensively, the reactivity of H2 and D2 exhibits an almost monotonic increase with increasing rotational quantum number J. Test calculations suggest that, for chemical accuracy (1 kcal/mol), the herringbone reconstruction of Au(111) should be modeled. [ABSTRACT FROM AUTHOR]

Accurately modeling surface temperature and surface motion effects is necessary to study moleculesurface reactions in which the energy dissipation to surface phonons can largely affect the observables of interest. We present here a critical comparison of two methods that allow to model such effects, namely, the ab initio molecular dynamics (AIMD) method and the generalized Langevin oscillator (GLO) model, using the dissociation of N2 on W(110) as a benchmark. AIMD is highly accurate as the surface atoms are explicitly part of the dynamics, but this advantage comes with a large computational cost. The GLO model is much more computationally convenient, but accounts for lattice motion effects in a very approximate way. Results show that, despite its simplicity, the GLO model is able to capture the physics of the system to a large extent, returning dissociation probabilities which are in better agreement with AIMD than static-surface results. Furthermore, the GLO model and the AIMD method predict very similar energy transfer to the lattice degrees of freedom in the non-reactive events, and similar dissociation dynamics. [ABSTRACT FROM AUTHOR]

The fundamental understanding of molecule-surface reactions is of great importance to heterogeneous catalysis, motivating many theoretical and experimental studies. Even though much attention has been dedicated to the dissociative chemisorption of N2 on tungsten surfaces, none of the existing theoretical models has been able to quantitatively reproduce experimental reaction probabilities for the sticking of N2 to W(110). In this work, the dissociative chemisorption of N2 on W(110) has been studied with both static electronic structure and ab initio molecular dynamics (AIMD) calculations including the surface temperature effects through surface atom motion. Calculations have been performed using density functional theory, testing functionals that account for the long range van der Waals (vdW) interactions, which were previously only considered in dynamical calculations within the static surface approximation. The vdW-DF2 functional improves the description of the potential energy surface for N2 on W(110), returning less deep molecular adsorption wells and a better ratio between the barriers for the indirect dissociation and the desorption, as suggested by previous theoretical work and experimental evidence. Using the vdW-DF2 functional less trapping-mediated dissociation is obtained compared to results obtained with standard semi-local functionals such as PBE and RPBE, improving agreement with experimental data at Ei = 0.9 eV. However, at Ei = 2.287 and off-normal incidence, the vdW-DF2 AIMD underestimates the experimental reaction probabilities, showing that also with the vdW-DF2 functional the N2 on W(110) interaction is not yet described with quantitative accuracy. [ABSTRACT FROM AUTHOR]

The theoretical description of methane dissociating on metal surfaces is a current frontier in the field of gas-surface dynamics. Dynamical models that aim at achieving a highly accurate description of this reaction rely on potential energy surfaces based on density functional theory calculations at the generalized gradient approximation. We focus here on the effect that the exchange-correlation functional has on the reactivity of methane on a metal surface, using CHD3 + Pt(111) as a test case. We present new ab initio molecular dynamics calculations performed with various density functionals, looking also at functionals that account for the van der Waals (vdW) interaction. While searching for a semi-empirical specific reaction parameter density functional for this system, we find that the use of a weighted average of the PBE and the RPBE exchange functionals together with a vdW-corrected correlation functional leads to an improved agreement with quantum state-resolved experimental data for the sticking probability, compared to previous PBE calculations. With this semi-empirical density functional, we have also investigated the surface temperature dependence of the methane dissociation reaction and the influence of the rotational alignment on the reactivity, and compared our results with experiments. [ABSTRACT FROM AUTHOR]