Scanning tunnelling microscopy (STM) and surface x-ray diffraction (SXRD) experiments are carried out to study the surface geometries of adsorbates on metal surfaces (see e.g. [1-3]). One recent example is the analysis of the oxygen adsorption site on Fe nanoislands deposited on oxygen precovered Fe(001): Fe/O/Fe(001) [3].  The STM image (left) shows Fe nanoislands (diameter ≈20-30 Å, height ≈2 Å, see lineprofile). The SXRD structure analysis  (right) reveals that the adsorption position of the oxygen atoms on the islands (i) is significantly expanded as compared to that on the Fe(001) terrace (t) (0.69 Å versus 0.42 Å), which is related to the Mesoscopic Misfit effect of the Fe nanoislands on the Fe(001) surface. Ab-initio calculations carried out by the theory department (Stepanyuk) confirm the experimental results.