The 4-b correction potential, ∆V 4-b , is a fit to a dataset of 3692 tetramer structures and corresponding reference energies computed at the CCSD(T)-F12/haTZ (aug-cc-pVTZ basis for O atoms and cc-pVTZ for H atoms) level of theory. This is the same data set we used to develop the 4-b component of the q-AQUA potential, 10 except that in this work we fit to the difference between CCSD(T) and TTM3-F 4-b energies rather than to direct 4-b energies.