Water dimer interactions are chosen for our calibration process given its appearance in many dedicated and general force fields. Furthermore, H 2 O is also small enough so that high accuracy ab initio methods can be conveniently used to generate enough reference data to calibrate our model. A total of 10000 water dimers are used to calibrate the XC functional. We separated them into what could be called non-hydrogen-bonded and hydrogen-bonded sets of 5000 configurations each. In the first one, the O -O distance is varied and in the second one the intermolecular O -H distance. Figure shows the start and end of the first set of configurations (∆L ∈ , θ ∈ [π, 3π/2]) and Figure shows the same for the second (∆L ∈ [2, 9.5], θ ∈ [-π/2, 0]). The configurations are sampled in a 25 × 200 grid for the angular and the distance components, respectively. ).