For the chemical systems considered, we obtain the Ψ λ FCI wavefunction for multiple λ values between 0 and 1 (uniform steps of 0.05 from 0 to 1). The λ-averaging is then performed using Eqs. 22, 35a, 35b, and 35c. This λ grid is more than sufficient since correlation energies computed through λ and spatial integrations [Eqs. 20 and 21] effectively introduce an error in correlation energies of ∼ 0 mH. Unless otherwise specified, we use the cc-pVTZ basis set (aug-cc-pVTZ for negative ions) for computing the energy densities from λ-FCI, which is sufficient for the correlation energy density analysis 4,18 of small systems. Furthermore, for all atoms/atomic ions used here, we employed an uncontracted basis set.