Being at the heart of heterogeneous catalysis including its several billion dollar business, the interaction of molecules with metal surfaces is of enormous interest. Solving the Schrödinger equation on steadily growing super-computing resources has paved the way for recent progress in ab-initio theoretical modeling, which does not require any parameters required from experiments: Current state-of-the-art descriptions of the interactions of diatomic molecules with static metal surfaces can come at chemical accuracy (~4.2 kJ/mol), but do rely on the Born-Oppenheimer approximation (BOA). While even large amounts of moving surface atoms can nowadays be modeled based on ab initio molecular dynamics (AIMD), going beyond the BOA still poses a conceptual challenge: Due to the absence of a band gap in metallic systems, excitations of electrons in form of electron-hole (eh) pairs come at essentially no energetic cost. Here, we aim to include the effect of these excitations in AIMD by augmenting Newton’s equations of motion with a friction force. Within a newly developed extension to the local density friction approximation, the friction coefficient is obtained “on-the-fly” during the dynamics. Aiming to resolve a long-standing controversy about the importance of eh-pairs for the latter, we apply this scheme to H2 on the Cu(111) as well as N2 on the W(110) surface.
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