Theory of electronic friction of adsorbates at metal surfaces: Methods and applications

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Electronic friction is a theoretical concept to treat non-adiabatic dynamics of atoms and molecules at metal surfaces in an approximate way. Non-adiabatic effects we have here in mind are due to the violation of the Born-Oppenheimer approximation, arising from the coupling of adsorbate modes to a continuum of metal excitations. Physical phenomena triggered by non-adiabaticity, which have already been considered in this project, are, among others: (i) The vibrational relaxation of vibrationally excited adsorbates and associated with it, the line broadening in vibrational spectroscopy. (ii) Energy transfer during and influences on, reactive and non-reactive molecule-surface scattering. (iii) Substrate-mediated femtochemistry at surfaces following excitation with ultrashort laser pulses. These phenomena are of general importance for spectroscopy, photochemistry, and energy transfer near metal surfaces.In this project the "Molecular Dynamics with Electronic Friction" (MDEF) method, in which classical equations of motion subject to frictional and fluctuating forces shall be further developed, and applied to selected examples of gas-surface dynamics. Planned methodological developments aim at including non-isotropic corrections and effects of surface atom motion for atomic, electronic friction coefficients, as well as the treatment of two time-dependent temperature baths (one for electrons and one for phonons) in "on the fly" AIMDEF ("Ab Initio MDEF") simulations.Applications concern non-trivial examples which are relevant for current experiments: (i) A systematic study of the vibrational relaxation of different atoms at surfaces and the role played by electronic and phononic relaxation channels. We also wish to study the dependence of these phenomena on the adsorption site, the type of metal, and surface structure. (ii) The vibrational relaxation and vibrational line broadening of frustrated translational modes of hydrocarbons adsorbed on "naked" and hydrogen-passivated, ruthenium surfaces shall be studied. (iii) The proposed phenomenon of "dynamic promotion" of a surface photoreaction shall be investigated for the example of laser-induced associative desorption of hydrogen and deuterium from a Ru(0001) surface. (iv) Finally, we aim at a deeper understanding of dynamical details during laser-driven femtochemistry of CO on Ru(0001), and their possible manipulation by variation of laser pulse parameters.