SAPT is a direct perturbative expansion for the A • • • B interaction energy, which we call E int,AB (or simply E int ) in order to distinguish it from the supramolecular energy-difference approach. Whereas ∆E int in Eq. ( ) is computed by energy difference, and is thus subject to basis-set superposition error (BSSE), the SAPT intermolecular interaction energy is not. In any EDA scheme that is based on a supramolecular calculation in a finite basis set, the BSSE is a spurious contribution that must be included somewhere. Furthermore, because SAPT is perturbative its accuracy is not beholden to a particular choice of density functional and can be systematically improved via higher orders in perturbation theory.