Bader charge analysis as carried out in section II E 2 is insensitive to the treatment of maxima families. This is because, for molecular systems, the electron density ρ has no extended maxima, only distinct point-like maxima near to each nucleus. However, this is not true for the Laplacian of the electron density ∇ 2 ρ. Indeed, the electronic shell structure of atoms leads to ∇ 2 ρ exhibiting alternating regions of charge concentration (∇ 2 ρ < 0) and charge depletion (∇ 2 ρ > 0) as one moves radially away from the nucleus . This naturally leads to spatiallyextended maximal shells of ∇ 2 ρ and derived quantities, as can be seen for a Neon atom in Fig. . The changes in the shell structure of the Laplacian upon bond formation will be discussed in Sec. II G 2.