A supramolecular nanostructure composed of four 4-acetylbiphenyl molecules and self-assembled on Au (111) was loaded with single Au adatoms and studied by scanning tunneling microscopy at low temperature. By applying voltage pulses to the supramolecular structure, the loaded Au atoms can be rotated and translated in a controlled manner. The manipulation of the gold adatoms is driven neither by mechanical interaction nor by direct electronic excitation. At the electronic resonance and driven by the tunneling current intensity, the supramolecular nanostructure performs a small amount of work of about 8 × 10(-21) J, while transporting the single Au atom from one adsorption site to the next. Using the measured average excitation time necessary to induce the movement, we determine the mechanical motive power of the device, yielding about 3 × 10(-21) W.

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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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