Convergence of SAPT0-D3MBJ interaction energy components for CO as a function of binding site size. The plot is generated by incrementally adding water molecules to CO from an extracted VH-BE Elst-class binding site (upper panel) and a VH-BE Disp-class binding site (lower panel). The interaction energy difference are with respect of the CO + W₃₅ limit (∆E_int = E_int(CO + W₃₅) − E_int (CO + W_X). The interaction energy in the Elst-class converges significantly faster than in the Disp-class binding site. The interaction energy is further decomposed into electrostatic, induction, dispersion and exchange contribution, of which the dispersion interaction is the slowest to converge. Therefore, selecting a binding site extract comprising 28 water molecules captures almost the totality of the interaction energy of CO + ASW.