Finally on this topic, we note that the rigorous separability of fragments has not been examined in detail for many MLPs. However, a common practical solution to the artificial fragment coupling is achieved by using a switching functions. That zero out the MLP in the asymptotic region and switch in another PES that is rigorously separable. This also permits adding accurate long-range interactions. An example of this is the recent PIP potential for the H 2 +NaCl potential. So, in short the original concern about non-physical coupling of fragments is in fact not a major issue.