The first term in this summand represents the AB energy computed using embedding charges for the full Nbody system, whereas the second term is a self-consistently polarized dimer computed using only charges on the dimer AB. In other words, E XSAPT,2B int,AB (AB) is a dimer XSAPT calculation that uses charge embedding, to be contrasted with a dimer SAPT calculation E SAPT int,AB , which does not. Energy components of the latter are what appear in Eq. (36).