ind,resp in place of E (2) ind in Eq. ( ) affords the best possible treatment of induction that is contained within second-order perturbation theory, but even this may be inadequate to describe the significant induction effects associated with hydrogen bonding. A supramolecular HF calculation contains much of those effects as it formally sums induction to infinite order in perturbation theory, albeit at zeroth order in Ŵ . As such, one may consider a correction for induction of the form δE HF = ∆E CP-HF int -E (10) elst + E (10) exch + E (20) ind,resp + E (20) exch-ind,resp (10) where ∆E is the counterpoise-corrected HF interaction energy, computed using the supramolecular approach [Eq. (2)]. The quantity defined in Eq. ( ) is known as the "δHF" correction and it is often added to SAPT0: