The spatially resolved average electron energy 𝜒̅ (𝒓) described by Eq. ( ) has also been extensively studied by Politzer, Murray and co-workers (who, unlike us, refer to it as the local ionization energy). Unfortunately, the average electron energy 𝜒̅ (𝒓) does not lend itself to conventional (QTAIM-like) quantum chemical topological analysis. One reason for the latter is that the topology of 𝜒̅ (𝒓) does not have critical points (maxima or minima) at nuclear positions. Therefore, it is not possible to meaningfully integrate out finite values from 𝜒̅ (𝒓) and associate them to a region of space. To see why, it suffices to consider an isolated molecule for which