As the main contribution to the scattering will come from the O-O correlation, we calculate the q = 0 structure factor of this atom-type pair, and correct it with the three previous corrections, again fitting the excluded volume as explained in the previous section. The middle plot shows how the excluded volume decreases as expected with increasing the density. The lowest plot shows how this translates into a linearly decreasing isothermal compressibility. Heuristically, the more we have already compacted the water, the less it is willing to be further compacted. As we are only using the O-O pair, and using the relatively simple TIP4P EW water model that e.g. employs rigid water molecules, we cannot expect a complete agreement with the experimental value, yet both the van der Vegt-and volume correction produces compressibilities very close to the experimental value of ambient water density at room temperature . This shows that the corrections not only make the integral converge, but also reproduce the experimental value, whereas the Perera correction seems to slightly overestimate it. This does not change whether we set κ lm from eq. 11 to the value found using our excluded-volume fitting method, or the first non-zero g lm (r) r-value, but we cannot rule out that further adjustments would increase the accuracy with respect to the experimental result. However, our result is consistent with the previous finding that the van der Vegt-and Perera-methods give different KBIs , most likely since the Perera-correction leaves the RDFs unchanged at shorter r-values, even though the sampled RDF should be corrected across all r.