Fig. 3. Top panel: the PES of a water trimer when one water is pulled away from the other two. Bottom panel: the percentage contribution of the Behler–Parrinello atom-wise energy, electrostatic energy and van der Waals energy to the binding energy between the water that is pulled away and the other two waters. The Behler–Parrinello atom-wise energy contributes most of the binding energy at short range and the electrostatic energy is the dominant contribution at long range.