Model systems of CO–W_2–3 used for the DFT energy and geometry benchmark. Rows show structure names and binding energies (BE). Numbers in parentheses indicate the ZPVE-corrected BE value. The water molecule acting as the H-bond donor to CO is labeled W_D. Characteristic distances are given in Å; energy values are in K. Atoms are color coded as follows: black for C, red for O, and white for H.