Room Temperature Hydrogen Atom Scattering Experiments Are Not a Sufficient Benchmark to Validate Electronic Friction Theory

TL;DR

This paper demonstrates that room temperature hydrogen atom scattering experiments are insufficient alone to validate electronic friction models, as similar results can be obtained from different theoretical approximations with varying accuracy.

Contribution

The study shows that common agreement between experiments and electronic friction models at room temperature can be coincidental, emphasizing the need for low-temperature experiments to distinguish theoretical approaches.

Findings

Agreement with experiments can be achieved with different theoretical models.

Homogeneous electron gas approximation overestimates friction near the surface.

Low-temperature experiments can reveal differences between models.

Abstract

In the dynamics of atoms and molecules at metal surfaces, electron-hole pair excitations can play a crucial role. In the case of hyperthermal hydrogen atom scattering, they lead to nonadiabatic energy loss and highly inelastic scattering. Molecular dynamics with electronic friction simulations where friction is computed under an isotropic homogeneous electron gas approximation have previously shown good agreement with measured kinetic energy loss distributions, suggesting that this level of theoretical description is sufficient to describe nonadiabatic effects of atomic scattering. In this work, we show that similar agreement with room temperature experiments can also be achieved with friction derived from density functional theory linear response calculations. The apparent agreement of the homogeneous electron gas approximation with experiment arises from a fortuitous cancellation of errors where friction is overestimated close to the surface and the spin transition is neglected. Only for scattering at low temperatures can both approximations be distinguished and differences rationalised in terms of the number of bounces of the atom on the surface. We identify the signatures of nonadiabatic energy loss of different levels of theory, which future low-temperature scattering experiments will be able to measure.