exch-disp in Eq. ( ) arises from the operator that enforces permutational antisymmetry between the monomer wave functions. The SAPT0 method affords a -C 6 /R 6 dispersion effect, albeit not a quantitative one, 246,255-258 as it is generally too attractive. An improved approach that includes monomer electron correlation is SAPT2+, for which the dispersion energy is