An ab initio molecular dynamics and correlation function approach to dissipative adsorbate vibrational spectroscopy

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The vibrations of atoms or molecules near solid surfaces are central to surface science. Probing the vibrations by steady-state and time-resolved spectroscopy provides "Fingerprints" which facilitate our understanding of elementary processes at surfaces, with the perspective to control and optimize them. The analysis of adsorbate vibrations by theory is often based on Normal Mode Analyses (NMA), which do not account for anharmonicity, temperature, mode couplings, and spectroscopic signals. They typically neglect also "Dissipation", i.e., relaxation caused by coupling to surface phonons and Electron Hole Pair (EHP) excitations, despite this can have a decisive influence on spectra. In this project we will go beyond NMA by using and extending Ab Initio Molecular Dynamics (AIMD) and AIMD with Electronic Friction (AIMDEF) methods, in combination with Time-Dependent Correlation Functions (TDCFs) for analysis and vibrational spectroscopy of adsorbates at surfaces. These methods account for all effects of above, give real-time information, have the potential to be extended to include quantum effects, and can be operated in an "on the fly'' mode without the need to precompute potential energy surfaces. This makes them applicable to complex systems which can hardly be treated otherwise. Specifically, we aim at a realistic modelling of vibration-phonon and / or vibration-EHP couplings and their influence on vibrational spectra, InfraRed (IR) and Vibrational Sum Frequency (VSF) spectra, both steady-state and time-resolved. Systems to be considered are hydrogen-covered silicon surfaces, water-covered metal and metal oxide surfaces, and metal surfaces in contact with hydrocarbons.