The failure of LDA and PBE functionals to stabilize the CO on the atop site is well-known. Nevertheless, where experiments are available we can compare the relative energies of the three adsorption sites. Additionally we present results for two other ground state properties: the site-resolved partial charges using a Bader analysis, and bond distances across the different functionals (Table ). In contrast to the total energy, bond lengths are remarkably uniform across functionals, and in good agreement with experiments. (This supports our argument that DFT is sufficient to determine structure, if not total energy.) Regarding Bader charge analysis, the most important finding is that partial charges vary wildly across functionals (Fig ). For the LDA functional, the CO was positively charged for all of the adsorption sites; the PBE and BEEF-vdW functionals resulted in a negatively charged CO for all the sites. Not only did the LDA destabilize the atomic site considerably compared to the hollow site, but it also exhibited the greatest polarity within the CO molecule. Indeed, the CO molecule became circa -2e and the Cu atom below it +2e. The magnitude of these interactions decreased from LDA to PBE to the BEEF-vdW calculations. By comparison, the bridging and hollow sites were inconsistent in the magnitude of the charge transfer across the Pt, C, and O atoms. Since the energy is a function of the charge, it is not surprising that the total energies based on DFT are unreliable. Forces are also controlled by charge (the density at the nucleus), yet surprisingly, the bond distances between the Pt-C, C-O bonds remain similar across the different functionals, with a relative difference of only 0.04Å. Intensity analysis of measured I-V curves in a dynamical low-energy electron diffraction (LEED) study provided considerable detail to surface CO-Pt (111) bonds. Indeed, the experimental uncertainty of the C-O bond 1.15±0.05 Å is broader than the variation in C-O bond lengths of all three site types (1.15-1.16 Å for atop CO, 1.17-1.18 Å for bridge CO, and 1.19 Å for hollow CO). A similar trend occurs for the Pt-C bond, wherein all three functionals can reproduce bond-lengths within the uncertainties of experiment.