Despite this, the ECP variant of our model noticeably underestimates the interaction energies, compared to accurateab initio calculations, of a water dimer in the O • • • H distance coordinate shown in the left panels of Figure . In contrast, the full electron variant of our model accurately predicts these interaction energies, however, it displays discernible numerical noise, despite 64-bit floating-point precision being used throughout our entire code. Similar numerical instability issues have also been reported in other studies that use comparable polarizable force field models. A close inspection of the water dimer displaced along the O • • • O distance coordinate shown the right panel of Figure , shows that both the full electron and ECP variants of our model reproduce its respective interaction energies with a fair degree of accuracy. Neither of the two variants of our model display unphysical oscillations through this distance coordinate. Like the O • • • H distance coordinate, the full electron variant of our model displays the same numerical noise in the O • • • O distance coordinate. Interestingly, for interatomic distances between 1.5 to 2.0 Å, compared to the reference ab initio reference data, our full electron fitted model underestimates energies. Nonetheless, for interatomic distances shorter than those illustrated in Figure , the accuracy of our ECP fitted model may diminish. This discrepancy arises from its inaccurate depiction of inner shell electrons, rendering it unsuited for extremely high-energy molecular dynamics simulations where such configurations might be more prevalent.