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Abstract

We investigate the thermal and electronic collective
fluctuations that contribute to the finitetemperature
adsorption properties of
flexible adsorbates on surfaces on the example of the molecular
switch azobenzene C₁₂H₁₀N₂ on the Ag(111) surface. Using first-principles molecular dynamics simulations
we obtain the free energy of adsorption that accurately accounts for entropic contributions,
whereas the inclusion of many-body dispersion interactions accounts for the electronic correlations
that govern the adsorbate binding. We find the adsorbate properties to be strongly entropy-driven,
as can be judged by a kinetic molecular desorption prefactor of 10²⁴ s^-1 that largely exceeds previously
reported estimates. We relate this effect to sizable
fluctuations across structural and electronic
observables. Comparison of our calculations to temperature-programmed desorption measurements
demonstrates that finite-temperature effects play a dominant role for
flexible molecules in contact
with polarizable surfaces, and that recently developed first-principles methods offer an optimal tool
to reveal novel collective behavior in such complex systems.