For the benchmarking of the auxiliary sets we define the density fitting error, ∆DF, as the difference between the total energy calculated with DF-HF and that with conventional HF. When molecules contain first-row elements (or hydrogen) the cc-pVnZ orbital basis sets were used for those elements, along with the matching cc-pVnZ/JKFit auxiliary sets. To place ∆DF in context, the BSIE of the molecules for the orbital basis sets has been calculated from CBS limits estimated with the extrapolation formula of Karton and Martin, 38 using the HF cc-pVQZ and cc-pV5Z energies. The density fitting error was also assessed for the scenario where the cc-pV(n+d)Z/JKFit auxiliary sets are used in conjunction with the cc-pVnZ-F12 orbital basis sets. The density fitting error in the dissociation energy (D e ), equilibrium bond length (r e ), and harmonic frequency (ω e ) of diatomic molecules at the HF level of theory was obtained by calculating the energy of seven near-equilibrium points (-0.3a 0 ≤ r -r e ≤ +0.5a 0 ) and fitting them with a sixth-order polynomial before a Dunham analysis.