The default settings for the GGA and hybrid calculations as regards the handling of the two-electron Coulomb repulsion integrals were employed. The resolution of identity approximation for the Coulomb energy (RI-J) was used for the BLYP calculations in combination with the def2/J auxiliary basis set. Computation of the second-order perturbation term in B2PLYP calculations were sped up using the resolution of identity approximation and the corresponding auxiliary basis set generated by the AutoAux procedure. To overcome the basis set superposition error, all the interaction energies presented in this paper are counterpoise-corrected according to the formulation of Boys and Bernardi. The basis set employed for the scan is the minimally augmented Karlsruhe basis set: ma-def2-TZVP. Our basis-set convergence study of the interaction energy of a bimolecular system, that consists of a water molecule noncovalently bonded to a model complex of Fe 2+ and two pyridine ligands (Fe[py] 2+ 2 ), indicates that augmenting the def2-TZVP basis set with only additional s and p functions yields accurate counterpoise-corrected DFT interaction energy within 0.01 eV (see section S1.1).