Electron–hole pair creation by atoms incident on a metal surface

We report an analytic potential energy surface (PES) based on several hundred DFT energies for H interacting with a Au(111) surface. Effective medium theory is used to fit the DFT data, which were obtained for the Au atoms held at their equilibrium positions. This procedure also provides an adequate treatment of the PES for displacements of Au atoms that occur during scattering of H atoms. The fitted PES is compared to DFT energies obtained from ab initio molecular dynamics trajectories. We present molecular dynamics simulations of energy and angle resolved scattering probabilities at five incidence angles at an incidence energy, E i = 5 eV, and at a surface temperature, T S = 10 K. Simple single bounce trajectories are important at all incidence conditions explored here. Double bounce events also make up a significant fraction of the scattering. A qualitative analysis of the double-bounce events reveals that most occur as collisions of an H-atom with two neighboring surface gold atoms. The energy losses observed are consistent with a simple binary collision model, transferring typically less than 150 meV to the solid per bounce.

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“…Note that these DFT energies were not used in the optimization procedure. These sites (labeled [11][12][13][14] are also shown in Fig. 1b.…”

Section: Presentation Of the New Potential Energy Surfacementioning

confidence: 81%

Toward Detection of Electron-Hole Pair Excitation in H-atom Collisions with Au(111): Adiabatic Molecular Dynamics with a Semi-Empirical Full-Dimensional Potential Energy Surface

Janke

Pavanello

Kroes

et al. 2013

Zeitschrift Für Physikalische Chemie

234

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“…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).…”

Section: Methodsmentioning

confidence: 99%

“…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). Here, the EHP excitation spectrum is related within the perturbation theory to the rate of the nonadiabatic energy transfer by the following equation (23):…”

Section: Methodsmentioning

confidence: 99%

“…LDFA combined with ab initio molecular dynamics (AIMD) has also been previously applied to study the associative desorption of diatomics at metal surfaces (18)(19)(20). Here, we extend the LDFA theory to describe the energy spectrum of the excited EHPs produced by the MD trajectories by implementing a forced oscillator model (FOM) (21)(22)(23). From reported barrier heights and barrier transmission probabilities of chemicurrent devices, we then determine what fraction of the excited electrons is detected as a chemicurrent.…”

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confidence: 99%

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

Kandratsenka

Jiang

Dorenkamp

et al. 2018

Proc. Natl. Acad. Sci. U.S.A.

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The Born-Oppenheimer approximation (BOA) provides the foundation for virtually all computational studies of chemical binding and reactivity, and it is the justification for the widely used "balls and springs" picture of molecules. The BOA assumes that nuclei effectively stand still on the timescale of electronic motion, due to their large masses relative to electrons. This implies electrons never change their energy quantum state. When molecules react, atoms must move, meaning that electrons may become excited in violation of the BOA. Such electronic excitation is clearly seen for: (i) Schottky diodes where H adsorption at Ag surfaces produces electrical "chemicurrent;" (ii) Au-based metal-insulator-metal (MIM) devices, where chemicurrents arise from H-H surface recombination; and (iii) Inelastic energy transfer, where H collisions with Au surfaces show H-atom translation excites the metal's electrons. As part of this work, we report isotopically selective hydrogen/deuterium (H/D) translational inelasticity measurements in collisions with Ag and Au. Together, these experiments provide an opportunity to test new theories that simultaneously describe both nuclear and electronic motion, a standing challenge to the field. Here, we show results of a recently developed first-principles theory that quantitatively explains both inelastic scattering experiments that probe nuclear motion and chemicurrent experiments that probe electronic excitation. The theory explains the magnitude of chemicurrents on Ag Schottky diodes and resolves an apparent paradox--chemicurrents exhibit a much larger isotope effect than does H/D inelastic scattering. It also explains why, unlike Ag-based Schottky diodes, Au-based MIM devices are insensitive to H adsorption.M ost theoretical studies of atoms and molecules interacting with metal surfaces are based on the Born-Oppenheimer approximation (BOA) (1). However, a growing number of examples have been found where electronic and nuclear degrees of freedom are strongly coupled in violation of the BOA (2-6). H-atom interactions at metals offer a remarkable opportunity to test non-BOA theories against experiment, since H-adsorptioninduced chemicurrent experiments (7-14) offer a direct measure of electronic excitation and H-atom inelastic scattering experiments (15) directly probe nuclear motion. In chemicurrent experiments, exothermic H interactions like adsorption and recombination produce hot electrons that pass over a potential barrier to be collected. Hence, the magnitude of the chemicurrent is dependent on both the reaction-induced production of hot electrons and the likelihood of transmission over the barrier. To reduce uncertainties associated with barrier transmission, the ratio of hydrogen-and deuterium-induced chemicurrent is often measured--H-induced chemicurrents are typically two to five times larger than those from D atoms (7,(11)(12)(13). H-atom surface scattering experiments yield H-atom translational energy loss distributions. The importance of H-atom translation to electronic exc...

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“…There have been several attempts to deduce a more detailed understanding of the e-h pair excitations behind frictional energy losses [24,40,41] by connecting the latter to a forced oscillator model (FOM) [42]. In essence, the FOM describes electronic excitations in the substrate through a collection of independent harmonic oscillators driven by an external force of identical functional form but different strength [41].…”

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confidence: 99%

Nonadiabatic Vibrational Damping of Molecular Adsorbates: Insights into Electronic Friction and the Role of Electronic Coherence

2017

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We present a perturbation approach rooted in time-dependent density-functional theory to calculate electron-hole (e-h) pair excitation spectra during the nonadiabatic vibrational damping of adsorbates on metal surfaces. Our analysis for the benchmark systems CO on Cu(100) and Pt(111) elucidates the surprisingly strong influence of rather short electronic coherence times. We demonstrate how in the limit of short electronic coherence times, as implicitly assumed in prevalent quantum nuclear theories for the vibrational lifetimes as well as electronic friction, band structure effects are washed out. Our results suggest that more accurate lifetime or chemicurrentlike experimental measurements could characterize the electronic coherence. DOI: 10.1103/PhysRevLett.119.176808 The tortuous ways in which kinetic and chemical energy is transferred between adsorbates and substrate atoms fundamentally govern the dynamics of surface chemical reactions, for instance, in the context of heterogeneous catalysis or advanced deposition techniques. For metal substrates, the two main energy dissipation mechanisms in this regard are the adsorbate interaction with lattice vibrations, i.e., substrate phonons, and the excitation of electronhole (e-h) pairs. The latter are attributable to the nonadiabatic coupling of nuclear motion to the substrate electronic degrees of freedom (d.o.f.) and seem to be substantial in order to rationalize an increasing number of experimental findings [1,2]. Important steps towards an accurate, yet efficient firstprinciples-based modeling of the energy uptake into phononic d.o.f. have recently been taken [3][4][5][6][7][8][9][10]. In contrast, the explicit description of e-h pair excitations and corresponding nonadiabatic couplings directly from first principles still poses a formidable challenge.In this regard, electronic friction theory (EFT) [11,12] has become a popular workhorse to effectively capture the effects of such nonadiabatic energy loss on the adsorbate dynamics in a computationally convenient way [13][14][15][16][17][18][19]. Inspired by vibrational lifetimes obtained via response theory [20] or Fermi's golden rule in the nuclear system [21], a Langevin equation for the nuclei emerges from a semiclassical picture implying complete electronic decoherence in terms of the Markov approximation [12]. This approach thus avoids an explicit propagation of the electron dynamics and concomitant ultrafast time scales by coarse-graining the effects into electronic friction forces linear in nuclear velocities. This enables an efficient combination even with density-functional theory (DFT) based ab initio molecular dynamics (AIMD) simulations on high-dimensional potential energy surfaces as required for surface dynamical studies [15,22,23].Independent of the particular recipe employed to obtain the electronic friction coefficients [12,14,17,20,24,25], however, the downside of the coarse-graining of the electron dynamics is that it precludes a more fundamental understanding of the underlying e-h pair excit...

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Electron–hole pair creation by atoms incident on a metal surface

Cited by 95 publications

References 32 publications

Toward Detection of Electron-Hole Pair Excitation in H-atom Collisions with Au(111): Adiabatic Molecular Dynamics with a Semi-Empirical Full-Dimensional Potential Energy Surface

Toward Detection of Electron-Hole Pair Excitation in H-atom Collisions with Au(111): Adiabatic Molecular Dynamics with a Semi-Empirical Full-Dimensional Potential Energy Surface

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

Nonadiabatic Vibrational Damping of Molecular Adsorbates: Insights into Electronic Friction and the Role of Electronic Coherence

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