The positions of the Hf atoms in the top layer and the vertical distance of CO were optimized using the BLYP functional and a 3x3x1 k-point mesh. Subsequently, the dissociation energy was calculated with BLYP, PBE, BP86, B3LYP, and PBE0 through single-point calculations on the BLYP-optimized geometry at the Γ point of both the slab with CO present and the slab without CO along with an isolated CO molecule.