For hydrogen-bonded systems, the hybrid SAPT0 + δHF approach is sometimes necessary to obtain high accuracy, even when third-order induction terms (beyond SAPT0) are included. However, mixing SAPT with an energy-difference approach has the potential to introduce BSSE into what is otherwise a BSSE-free formalism. As such, ∆E CP-HF int should always be evaluated using counterpoise (CP) correction, as indicated by the notation. Even for self-consistent field (SCF) calculations, the CP correction is not negligible unless basis sets of at least quadruple-ζ quality are employed. Substituting Eq. ( ) into Eq. ( ) affords