Ab initio molecular dynamics calculations on scattering of hyperthermal H atoms from Cu(111) and Au(111)

Abstract

In-plane structure and ordering at liquid sodium surfaces and interfaces from ab initio molecular dynamics J. Chem. Phys. 127, 134703 (2007); 10.1063/1.2781388Publisher's Note: "Ab initio molecular dynamics simulation of the H/InP(100)-water interface" [J. Chem. Phys. 117, 872 (2002) Energy loss from the translational motion of an atom or molecule impinging on a metal surface to the surface may determine whether the incident particle can trap on the surface, and whether it has enough energy left to react with another molecule present at the surface. Although this is relevant to heterogeneous catalysis, the relative extent to which energy loss of hot atoms takes place to phonons or electron-hole pair (ehp) excitation, and its dependence on the system's parameters, remain largely unknown. We address these questions for two systems that present an extreme case of the mass ratio of the incident atom to the surface atom, i.e., H + Cu(111) and H + Au(111), by presenting adiabatic ab initio molecular dynamics (AIMD) predictions of the energy loss and angular distributions for an incidence energy of 5 eV. The results are compared to the results of AIMDEFp calculations modeling energy loss to ehp excitation using an electronic friction ("EF") model applied to the AIMD trajectories, so that the energy loss to the electrons is calculated "post" ("p") the computation of the AIMD trajectory. The AIMD calculations predict average energy losses of 0.38 eV for Cu(111) and 0.13-0.14 eV for Au(111) for H-atoms that scatter from these surfaces without penetrating the surface. These energies closely correspond with energy losses predicted with Baule models, which is suggestive of structure scattering. The predicted adiabatic integral energy loss spectra (integrated over all final scattering angles) all display a lowest energy peak at an energy corresponding to approximately 80% of the average adiabatic energy loss for non-penetrative scattering. In the adiabatic limit, this suggests a way of determining the approximate average energy loss of non-penetratively scattered H-atoms from the integral energy loss spectrum of all scattered H-atoms. The AIMDEFp calculations predict that in each case the lowest energy loss peak should show additional energy loss in the range 0.2-0.3 eV due to ehp excitation, which should be possible to observe. The average non-adiabatic energy losses for non-penetrative scattering exceed the adiabatic losses to phonons by 0.9-1.0 eV. This suggests that for scattering of hyperthermal H-atoms from coinage metals the dominant energy dissipation channel should be to ehp excitation. These predictions can be tested by experiments that combine techniques for generating H-atom beams that are well resolved in translational energy and for detecting the scattered atoms with high energy-resolution. © 2014 AIP Publishing LLC.

Quantum and classical dynamics of reactive scattering of H2 from metal surfaces

“…156,297 The reason is that the energy dissipation due to friction not only depends on the metal electronic density sampled by the molecule, but also its velocity. 301,302 However, in principle energy dissipation processes occurring at the surface side of the barriers should not affect the dissociative chemisorption and scattering probabilities of H 2 , which is why strong non-adiabatic effects on these observables are typically not seen. The above might seem to suggest that ehp excitation has little role to play in dissociative chemisorption of H 2 on metal surfaces.…”

Inelastic H and D atom scattering from Au(111) as benchmark for theory

“…[8][9][10][11][12] However, the only experimental observable here is the chemicurrent that is strongly dependent on the design of the sensor making comparison to theory difficult. Further theoretical studies focused on inelastic scattering [13][14][15] and diffusion. 16 Recently, we performed inelastic scattering experiments of H and D atoms from metal surfaces.…”

Unified description of H-atom–induced chemicurrents and inelastic scattering

“…H-atom surface scattering experiments yield H-atom translational energy loss distributions. The importance of H-atom translation to electronic excitation could be inferred by comparing energy loss for H-atom collisions with metals and insulators and by comparing experiment to theory (15,16). As we will show below, D-atom energy loss on Au and Ag is nearly identical to that of H, introducing an apparent paradox between chemicurrent and inelastic scattering observations.…”