Energetics of hydrogen chemisorbed on Cu(110): A first principles calculations study

Embedded atom method potential for hydrogen on palladium surfaces

The development of transferable interatomic potentials for the diffusion of hydrogen on palladium surfaces can be of significant value for performing molecular simulations. These molecular simulations can, in turn, lead to a better understanding of palladium-hydrogen interactions at the atomic scale. Here, we have built upon previous work to develop an analytical palladium-hydrogen-embedded atom method (EAM) potential to better describe the potential energy surface for hydrogen on palladium surfaces. This EAM potential reproduces minima and transition states calculated with density functional theory for hydrogen on Pd(111) and Pd(110) surfaces. Additionally, this potential was tested by simulating the long timescale dynamics of hydrogen adsorbed on Pd(111). Our simulations show a barrier of ca. 0.49 eV for hydrogen diffusion into the bulk of Pd(111), which is consistent with experimental results.

Theoretical Insights into Unexpected Molecular Core Level Shifts: Chemical and Surface Effects

A set of density-functional theory based tools is employed to elucidate the influence of chemical and surface-induced changes on the core level shifts of X-ray photoelectron spectroscopy experiments. The capabilities of our tools are demonstrated by analyzing the origin of an unpredicted component in the N 1s core level spectra of metal phthalocyanine molecules (in particular ZnPc) adsorbed on Cu(110). We address surface induced effects, such as splitting of the lowest unoccupied molecular orbital or local electrostatic effects, demonstrating that these cannot account for the huge core level shift measured experimentally. Our calculations also show that, when adsorbed at low temperatures, these molecules might capture hydrogen atoms from the surface, giving rise to hydrogenated molecular species and, consequently, to an extra component in the molecular core level spectra. Only upon annealing, and subsequent hydrogen release, would the molecules recover their nominal structural and electronic properties.

Influence of aggregation, defects, and contaminant oxygen on water dissociation at Cu(110) surface: A theoretical study

The DFT-PW91 slab model approach is employed to investigate the influence of aggregation, surface defects, and contaminant oxygen on water dissociation on Cu(110) at low temperatures. The dissociation barriers of water in various aggregate states are calculated in the range of 60-75 kJ/mol on the clean surfaces, in nice agreement with the experimentally determined values. It is revealed that the aggregation of water shows no propensity to reduce the activation barrier for the O-H bond breaking on Cu(110), at variance with the water chemistry on Ru(0001). The calculated activation energy on Cu(211) which is the most active stepped surface investigated is equal to the value on the (110) surface, indicating that the hydroxyl groups observed on Cu(110) at low temperatures may not stem from surface defects. The coadsorbed oxygen, whether as a "spectator" or a "participant," facilitates the water dissociation both kinetically and thermodynamically.

Adsorption of atoms on cu surfaces: a density functional theory study

The chemisorption of atoms (H, N, S, O, and C) on Cu surfaces has been systematically studied by the density functional theory generalized gradient approximation method with the slab model. Our calculated results indicate that the orders of the adsorption energy are H < N < S < O < C on Cu(111) and H < N < O < S < C on Cu(110) and Cu(100). Furthermore, the adsorption energies of the given atoms on Cu(100) are larger than those on Cu(111) and Cu(110). The preferred adsorption sites are a 3-fold hollow site on Cu(111) and a 4-fold hollow site on Cu(100), but the preferred adsorption sites on Cu(110) are different for different adatoms. The energy, as well as the geometry, is in good agreement with the experimental and other theoretical data. In addition, this study focuses on the electronic and geometric properties of the metal-atom (M-A) bond to explain the difference in adsorption energies among adatoms. A detailed investigation of the density of states curves explains the nature of the most stable site. Finally, we test the effect of the coverage and find that the surface coverage has no influence on the preferred adsorption sites of the given adatoms on Cu(110) with the exception of hydrogen and oxygen, but has much influence on the value of the adsorption energy.

Theoretical study of hydrogen dissociative adsorption on the Cu(110) surface

We have calculated the six-dimensional (6D) potential energy surface for H2 in front of a frozen Cu(110) surface using density functional theory for 22 H2-surface configurations and the corrugation reducing procedure to interpolate between them. We carry out classical trajectory calculations on the dissociative adsorption process and find excellent agreement with measurements. We find that it is of prominent importance to account for the rovibrational state distribution in the incident H2 beam. A straightforward analysis leads to the conclusion that the motion along the surface does not play an appreciable role in the dynamics whereas the dynamical role of molecular rotation is crucial. The latter fact precludes any interpretation of dissociation in terms of a static concept such as "barrier distributions."