Spin-polarized electronic structure calculations for the CO/Co(0001) system were performed with VASP using the BEEF-vdW exchange-correlation functional. An optimized lattice constant of a = 2.50 Å and c = 4.06 Å, which is in good agreement with the experimental lattice constant , was used for the 3 × 3 unit cell that was sampled with a (5×5×1) k-point grid. The plane-wave kinetic energies were expanded to 40 Ry, applying a first-order Methfessel-Paxton smearing with an electron temperature of 0.1 eV.