to quantify the flow of charge from A to B, which amounts to a Löwdin-style partition of ∆P. The quantity Ω A→B is a CT index in the spirit of l A→B but corrected to take proper account of the nonorthogonal AO basis set. A Mulliken-style partition has also been formulated, in the spirit of Eq. (4.8), however Löwdin populations are generally more stable and free of negative population artifacts. That said, the value of Ω A→B certainly depends on the choice of AO basis set, just like any Löwdin population analysis. The method based on Eq. (4.9) has been called fragment transition density analysis, because in the case of a correlated wave function one could imagine using the TDM in place of ∆P. For TD-DFT there is no distinction, although one could substitute ∆P rlx in place of ∆P, thereby using the relaxed density to understand charge flow. In view of the discussion in Section 2.3, this is probably the better approach for quantitative analysis of CT states.