A simpler procedure is based on constrained (c)DFT, a general technique in which the KS equation is solved in the presence of a constraint that forces a stipulated group of atoms to integrate to a user-specified number of electrons. 159 (There is some variability in how the constraint is implemented and our approach is documented elsewhere. ) Using cDFT, one can define a CT-free reference state in which the A • • • B complex is assembled in space at the geometry of the dimer, and its KS-DFT energy is computed under the constraint that both monomers contain an integer number of electrons. Thus, orbitals are polarized but cannot transfer any (net) charge. Relaxing this constraint defines E CT (as the cDFT → DFT relaxation energy), which is subtracted from a SAPT-based calculation of E ind to define E pol . For H 3 N• • • BH 3 , Fig. shows that this definition is exquisitely stable with respect to basis set, with a very minor change in E CT between double-and triple-ζ basis sets but no change thereafter. This is consistent with the fact that DFT densities tend to be almost converged in double-ζ basis sets and well-converged in triple-ζ basis sets.