Electron-hole spectra created by adsorption on metals from density functional theory

Abstract

Nonadiabaticity in adsorption on metal surfaces gives rise to a number of measurable effects such as chemicurrents and exoelectron emission. Here we present a quantitative theory of chemicurrents on the basis of ground-state density functional theory ͑DFT͒ calculations of the effective electronic potential and the Kohn-Sham band structure. Excitation probabilities are calculated both for electron-hole pairs and for electrons and holes separately from first-order time-dependent perturbation theory. This is accomplished by evaluating the matrix elements ͑between Kohn-Sham states͒ of the rate of change of the effective electronic potential between subsequent ͑static͒ DFT calculations. Our approach is related to the theory of electronic friction, but allows for direct access to the excitation spectra. The method is applied to adsorption of atomic hydrogen isotopes on the Al͑111͒ surface. The results are compatible with the available experimental data ͑for noble metal surfaces͒; in particular, the observed isotope effect in H versus D adsorption is described by the present theory. Moreover, the results are in qualitative agreement with computationally elaborate calculations of the full dynamics within time-dependent density functional theory, with the notable exception of effects due to the spin dynamics. Being a perturbational approach, the method proposed here is simple enough to be applied to a wide class of adsorbates and surfaces, while at the same time allowing us to extract system-specific information.

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

“…Attempts to theoretically describe chemicurrents have been previously reported (21)(22)(23)(34)(35)(36)(37). In this work, we employed an FOM to obtain the energy spectrum of excited electrons that result from H/D atom collisions at the metal (21)(22)(23).…”

Energy Dissipation during Diffusion at Metal Surfaces: Disentangling the Role of Phonons versus Electron-Hole Pairs

“…In terms of the motion through the surface electron density, the situation is thus highly comparable to vibrational dynamics, an area where the LDFA has been shown to perform quantitatively [22]. Correspondingly, we expect this level of theory to provide a reliable assessment of the relative amount of electronic friction, even though it would be conceptually interesting to compare to higher-level theories that for instance account for tensorial aspects of friction [50] or that additionally provide the explicit ℎ-pair excitation spectra [12,51]. We further note that similar to the findings for adsorbate vibrations [22], a key element in the use of the simple LDFA scheme is the appropriate determination of the host embedding density experienced by the adsorbate.…”

Vibrational deexcitation and rotational excitation of H2 and D2 scattered from Cu(111): Adiabatic versus non-adiabatic dynamics

“…15 Motivated by this controversy, an important number of theoretical methods that include electronic excitations have been recently developed. [16][17][18][19][20][21][22][23][24] In some cases, non-adiabatic dynamics based on low-dimensional calculations has resulted in overestimation of the effects associated with e-h pair excitations. For example, for N 2 /Ru(0001) it was claimed, 16 based on low-dimensional non-adiabatic calculations, that the huge discrepancy between low-dimensional adiabatic calculations and experiment was mostly due to e-h pair excitations, whereas a subsequent adiabatic high-dimensional dynamics study 25,26 showed that most of the discrepancy vanishes when the six degrees of freedom of the molecule are taken into account in the dynamics.…”