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

In the dynamics of\natoms and molecules at metal surfaces, electron–hole\npair excitations can play a crucial role. In the case of hyperthermal\nhydrogen atom scattering, they lead to nonadiabatic energy loss and\nhighly inelastic scattering. Molecular dynamics with electronic friction\nsimulation results, based on an isotropic homogeneous electron gas\napproximation, have previously aligned well with measured kinetic\nenergy loss distributions, indicating that this level of theoretical\ndescription is sufficient to describe nonadiabatic effects during\nscattering. In this study, we demonstrate that friction derived from\ndensity functional theory linear response calculations can also describe\nthe experimental energy loss distributions, although agreement is\nslightly worse than for the simpler isotropic homogeneous electron\ngas approximation. We show that the apparent agreement of the homogeneous\nelectron gas approximation with experiment arises from a fortuitous\ncancellation of errors as friction is overestimated close to the surface\nand the spin transition is neglected. Differences in frictional treatment\naffect single, double, and multibounce scattering trajectories in\ndistinct ways, altering the shape of low-temperature energy loss distributions.\nThese distinctions are largely absent at room temperature but may\nbe measurable in future low-temperature scattering experiments.