The adsorption structure of the molecular switch azobenzene on Ag(111) is
investigated by a combination of normal incidence x-ray standing waves and
dispersion-corrected density functional theory. The inclusion of nonlocal
collective substrate response (screening) in the dispersion correction
improves the description of dense monolayers of azobenzene, which exhibit a
substantial torsion of the molecule. Nevertheless, for a quantitative
agreement with experiment explicit consideration of the effect of vibrational
mode anharmonicity on the adsorption geometry is crucial
