To conclude the discussion on the accuracy of the Padéinterpolated e Padé c , we note note again that this approach requires only one FCI calculation at λ = 1 (see Sec. V A), compared to approximately 20 FCI calculations over the full λ-grid for the exact e c (r). While this represents a significant cost reduction, the need for an expensive FCI calculation at λ = 1 makes e Padé c unsuitable as a direct approximation. Nevertheless, if one requires e c (r) ).