DFT-functional benchmark on the tetrameric structures; orange and blue series account respectively for results with 6-311+G(d,p) and aug-cc-pVTZ as basis set – left column: difference with respect to CCSD(T) value. CCSD(T) reference BE and BSSE correction values are given explicitly; right column: relative difference with respect to CCSD(T) value in%. Graphs are going by pairs (raw), with the first raw being attributed to NH₃, the second to CO and the third to CH₄. The last raw gives the MARDs over the three adsorbates.