Also for CO adsorption on compact Pt3 trimers (Figure ), adsorption of a single CO on different sites of the trimer (on-top, bridge or threefold hollow) results in very small differences of the adsorption energy by at most 30 meV. Interestingly, for adsorption on the less symmetric on-top and bridge sites, there is a small tilt off from the vertical configuration, indicating that the respective other Pt surface atom(s) have a small effect on the adsorption geometry. Addition of a second and a third COad, which both adsorb on on-top sites, leads to changes of the mean CO adsorption energy by about 30 meV per CO, which is very close to the changes observed before for increasing CO adsorption on a Pt2 dimer.