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The dissociative chemisorption (DC) of O2on Cu(111) has been extensively studied by both theory and experimentation. Different experiments disagree on the underlying mechanisms (direct or indirect) for the sticking of O2. Thus far, studies based on density functional theory (DFT) favor the indirect mechanism. However, DFT has not fully resolved the discussion as DFT based on the generalized gradient approximation (GGA) has always substantially overestimated the reactivity and sticking probabilities of O2on Cu(111) and other Cu surfaces. Recent work indicated that this overestimation is due to the failure of GGA DFT to describe molecule–metal systems where the charge transfer energy (ECT), i.e., the work function of the metal surface minus the electron affinity of the molecule, is below 7 eV. O2+ Cu(111) is one such system. This work presents computed sticking probabilities for O2+ Cu(111) based on the HSE06-1/2x-VdWDF2 screened hybrid van der Waals density functional (DF), which is applied self-consistently. A six-dimensional static potential energy surface (PES) was constructed using the corrugation-reducing procedure, keeping the surface atoms fixed. This PES was used to perform quasi-classical trajectory calculations to compute the sticking probabilities of O2+ Cu(111). For the first time, we present DFT-based sticking probabilities that underestimate the experimental sticking probabilities. While reproducing the experimental results would have been even more desirable, the fact that we found a DF which underestimates the measured sticking probabilities means that a DF using a lower fraction of exact exchange will most likely describe the O2+ Cu(111) system with high accuracy. Furthermore, our work shows evidence for the presence of both indirect and direct dissociative chemisorptions. The indirect precursor-mediated mechanism occurs for low-incidence energy O2. The mechanism is supplanted by a direct dissociative mechanism at higher incidence energies. Lastly, our work suggests that the Cu surface temperature may also affect the dissociation mechanism, but this still needs further verification with a different theoretical framework that allows for the simulation of surface temperature.

Accurate 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 S0measured 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.

We present the results of classical trajectory calculations of the adsorption of thermal CO on the surface of compact amorphous water ice, with a view to understanding the processes governing the growth and destruction of icy mantles on dust grains in the interstellar medium and interpreting solid CO infrared spectra. The calculations are performed at normal incidence, for Ei= 0.01 eV (116 K) and surface temperature Ts= 90 K. The calculations predict high adsorption probabilities (~1), with the adsorbed CO molecules having potential energies ranging from -0.15 to -0.04 eV with an average energy of -0.094 eV. In all the adsorbing trajectories, CO sits on top of the surface. No case of CO diffusion inside the ice or into a surface valley with restricted access was seen. Geometry minimizations suggest that the maximum potential energy of adsorbed CO (-0.155 eV) occurs when CO interacts with a “dangling OH” group, associated with the 2152 cm-1band seen in laboratory solid-state CO spectra. We show that relatively few “dangling OH” groups are present on the amorphous ice surface, potentially explaining the absence of this feature in astronomical spectra. CO also interacts with “bonded OH” groups, which we associate with the 2139 cm-1infrared feature of solid CO. Our results for CO adsorption on amorphous ice are compared with those previously obtained for CO adsorption to crystalline ice. The implications of the spectroscopic assignments are discussed in terms of the solid-CO infrared spectra observed in interstellar regions. Using the Frenkel model, the lifetime τfor which CO may remain adsorbed at the surface is calculated. At temperatures relevant to the interstellar medium, i.e. 10 K, it is longer than the age of the universe, but decreases dramatically with increasing Ts, such that at Ts= 90 K, τ= 300 ns. The pre-exponential factor $\tau_{\nu}$used in the Frenkel model is found to be 0.95 ±0.02 ps. These data are compared to recent experimental results. The astrophysical implications of these calculations are discussed, with particular reference to the CO binding sites identified on amorphous ice surfaces, their adsorption energies, probabilities and lifetimes.

Iedere ouder ervaart bij tijd en wijle weleens stress bij het opvoeden. Wanneer deze stress niet van tijdelijke aard is of wanneer de stress erg hoog wordt, kan professionele hulp ingeschakeld worden. Het vaststellen van de aard en ernst van de opvoedingsstress is dan van belang. De Opvoedingsbelastingvragenlijst (OBVL) is een recent ontwikkeld instrument hiervoor. De uitkomsten van het hier beschreven onderzoek geven positieve aanwijzingen voor de betrouwbaarheid en validiteit van de OBVL. De OBVL is ontwikkeld voor instellingen voor jeugdzorg, maar is ook op andere terreinen van zorg voor kinderen goed bruikbaar. De lijst is geschikt voor screening, diagnostiek en evaluatie van behandelingen.

Diffraction of H2from surfaces is considered to be a useful tool to characterize molecule/surface interactions and surface topology. In this work, we have studied diffraction of H2from a strained pseudomorphic monolayer of Cu deposited on Ru(0001), both experimentally and theoretically. Our experimental measurements show a remarkable diffraction probability, both in-plane and out-of-plane. In particular, we observe for the first time third-order diffraction peaks. These striking experimental results have been analyzed by performing theoretical simulations, using both quantum and quasi-classical dynamics methods. Taking into account the relationship between diffraction (quantum phenomenon) and reflection (classical observable), we have performed a classical analysis of a meaningful set of classical trajectories. This analysis reveals that for H2/Cu/Ru(0001) diffracted molecules practically explore the entire surface unit cell and are able to get close to the surface, thus favoring high-order diffraction.

We have constructed first principle based six-dimensional (6D) potential energy surfaces (PESs) describing the interaction of H2with Cu(111) obtained by interpolation of a set of density functional theory (DFT) total energy data. The DFT calculations have been performed within the generalized gradient approximation (GGA) framework. In applying the GGA we have tested the two exchange−correlation (XC) functionals most popular in surface science, i.e., the PW91 and RPBE functionals. The interpolation of the PW91 PES has been performed using two different methods, the corrugation reducing procedure (CRP), which has been proven to be one of the most successful interpolation methods to build 6D PESs, and the modified Shepard (MS) interpolation method, a very promising method to build high dimensional (nD) PESs, which is computationally cheaper than the CRP. We show that, in spite of the difference between the CRP-PES and the MS-PES and the inaccuracies found in the latter, quantum and classical reaction and scattering probabilities obtained for both PESs are very similar. We also show that PW91 predicts higher reactivity than RPBE, due to the presence of lower energy dissociation barriers in the PW91-PES. The differences between the PW91-PES and the RPBE-PES are also reflected in the vibrational excitation and rotational excitation probabilities, and the diffraction patterns.

The photo-oxidation of water on the rutile TiO2(110) surface is investigated using density functional theory calculations. A stable (TiO2)26cluster is used to model the rutile bulk and (110) surface. A model in which every reactant state contains a photoinduced positively charged cluster and every product state contains a neutral cluster plus a proton is used to study the photo-oxidation of water. In each reaction step, a photoinduced hole localized in the surface reacts with an adsorbed atom or molecule surrounded by water leading to a neutral cluster, a proton surrounded by water, and a product vacancy, adsorbed atom, or molecule. According to this model the illumination of the TiO2(110) surface with light provides enough overpotential for the photo-oxidation to proceed spontaneously.

The oxidation and photo-oxidation of water on the rutile TiO 2(110) surface is investigated using density functional theory (DFT) calculations. We investigate the relative stability of different surface terminations of TiO 2interacting with H 2O and analyze the overpotential needed for the electrolysis and photoelectrolysis of water. We found that the most difficult step in the splitting of water process is the reaction of a H 2O molecule with a vacancy in the surface to form an adsorbed hydroxyl group (OH*). Comparison to experiment shows that the computed overpotential for O 2evolution (0.78 V) is available under the experimental conditions required for both oxygen and hydrogen evolution.

We present results of classical trajectory calculations on the sticking of hydrogen atoms to the basal plane (0001) face of crystalline ice, Ih. The sticking probability is found to decrease with both incidence energy (Ei) and surface temperature (Ts). At the surface temperatures studied, the sticking probability can be fitted to a simple decay function:  Ps = 1.5 e^-Ei^(K)/175 at Ts = 10 K, and Ps = 0.85 e^-Ei^(K)/175 at Ts = 70 K. In the trapped state, the adsorbed hydrogen atom is located on top of the ice surface, over the center of a surface hexagonal ring, interacting with all water molecules forming the ring. The calculated physisorption energy of the adsorbed atom is approximately 400 ± 50 K. The results of our calculations are compared with the experimental and theoretical data for amorphous ice surfaces. At Ts = 10 K, our values for the sticking probability are higher than those of Buch and Zhang [Buch, V.; Zhang, Q. Astrophys. J. 1991, 379, 647], which is attributed to differences in surface topology. Our sticking probability values are lower than those of Masuda et al. [Masuda, K.; Takahashi, J.; Mukai, T. Astron. Astrophys. 1998, 330, 243], which we attribute to an incorrect implementation of the H−H2O potential in their work. The experimental results available on hydrogen formation on amorphous ice are in good agreement with our results, if the assumption is made that all H-atoms that stick will recombine. Our calculations then suggest that the formation of H2 through recombination of H-atoms adsorbed on the surface is efficient enough to compete with the cosmic destruction of H2.

Recent theoretical progress in gas−surface reaction dynamics, a field relevant to heterogeneous catalysis, is described. One of the most fundamental reactions, the dissociative chemisorption of H2 on metal surfaces, can now be treated accurately using quantum mechanics. Density functional theory is used to compute the molecule−surface interaction, and the motion of the hydrogen atoms is simulated using quantum dynamics, modeling all six molecular degrees of freedom. Theory is in good quantitative agreement with molecular beam experiments, offering useful interpretations, and allowing reliable predictions. The success of the approach calls for extensions to larger systems, such as dissociative chemisorption of polyatomic molecules.

Accurate barriers for rate controlling elementary reactions on metal surfaces are key to understanding, controlling, and predicting the rate of heterogeneously catalyzed processes. While barrier heights for gas phase reactions have been extensively benchmarked, dissociative chemisorption barriers for the reactions of molecules on metal surfaces have received much less attention. The first database called SBH10 and containing 10 entries was recently constructed based on the specific reaction parameter approach to density functional theory (SRP-DFT) and experimental results. We have now constructed a new and improved database (SBH17) containing 17 entries based on SRP-DFT and experiments. For this new SBH17 benchmark study, we have tested three algorithms (high, medium, and light) for calculating barrier heights for dissociative chemisorption on metals, which we have named for the amount of computational effort involved in their use. We test the performance of 14 density functionals at the GGA, GGA+vdW-DF, and meta-GGA rungs. Our results show that, in contrast with the previous SBH10 study where the BEEF-vdW-DF2 functional seemed to be most accurate, the workhorse functional PBE and the MS2 density functional are the most accurate of the GGA and meta-GGA functionals tested. Of the GGA+vdW functionals tested, the SRP32-vdW-DF1 functional is the most accurate. Additionally, we found that the medium algorithm is accurate enough for assessing the performance of the density functionals tested, while it avoids geometry optimizations of minimum barrier geometries for each density functional tested. The medium algorithm does require metal lattice constants and interlayer distances that are optimized separately for each functional. While these are avoided in the light algorithm, this algorithm is found not to give a reliable description of functional performance. The combination of relative ease of use and demonstrated reliability of the medium algorithm will likely pave the way for incorporation of the SBH17 database in larger databases used for testing new density functionals and electronic structure methods.

We consider the scattering of H2 from surfaces for two benchmark systems. The system H2 + LiF(001) is the classical example of hydrogen scattering off an ionic surface. Quantum dynamical calculations employing a new model potential and experiments have shown that the electrostatic interaction between the molecule's quadrupole moment and the surface ions has a crucial influence on the scattering in this system. The results suggest that the ionicity of the surface ions in ionic surfaces can be probed by scattering H2 of these surfaces, for instance, by measuring the differences between diffraction of cold p-H2 and cold o-H2. The system H2 + Cu is the classic example of activated dissociative chemisorption. It is now possible to perform quantum dynamical calculations on fully activated dissociative chemisorption in which all molecular degrees of freedom are treated without dynamical approximations, as here illustrated for H2 + Cu(100). This development makes it possible to evaluate the accuracy of electronic structure methods for molecule−surface interactions, to help interpret trends in the reactivity observed experimentally, and to arrive at new predictions for experiments.

A structural study of the surface of an ultrathin ice film grown on a Pt(111) substrate was performed using dynamical low-energy electron diffraction (LEED) at 90 K, together with total-energy calculations and molecular dynamics (MD) simulations. This ice film exhibits the common hexagonal phase Ih and exposes the (0001) surface without reconstruction. The surface is terminated as a full-bilayer that maximizes the number of surface hydrogen bonds as confirmed by our total-energy calculations. Both LEED and MD simulations find that the outermost water molecules have enhanced vibrational amplitudes making them practically undetectable by LEED even at 90 K. MD simulations of the half-bilayer terminated surface yield results inconsistent with the LEED findings, thus excluding this model.