A very different approach from the fragmented-basis is the many-body one. This approach has a long history in atomic physics, notably for Si and using models for these terms. A recent application to the non-covalent Ar atom 3-b interaction 49 is also noteworthy. For non-covalent molecular applications, the "bodies" are molecules. A notable example is for water potentials, where the total energy of N H 2 O monomers is given by 15,41