Quite apart from DFT-based EDAs, the SAPT framework is much older and has its basis in many-body theory. It uses isolated-monomer wavefunctions as a zeroth-order starting point, then computes the intermolecular interaction using a form of perturbation theory. For a noncovalent dimer A • • • B, this amounts to a partition ĤAB = FA + FB Ĥ0 +ξ ( ŴA + ŴB )