Charge concentration (∇ 2 ρ < 0), or depletion (∇ 2 ρ > 0), is most relevant to chemistry when it occurs in the valence region of an atom in a molecule. In particular, it has been noted that the maxima of valence charge concentration (depletion) correlate with the active regions for electrophilic (nucleophilic) attack . Critical networks spanning these maxima form the valence shell charge concentration/depletion (VSCC/D) graphs . Such graphs can be easily examined by constructing the . Values of the charge density (in e/bohr 3 ) for each bond critical point identified in benzene for named grid sizes in QUEST. The values can be clearly seen to be split into groups of 4 and 2 as a result of the DFT grid breaking sixfold symmetry. The level of theory is as specified in Sec. II E 1 and results using QChem v5.0 and the Multiwfn package v3.8 are also given. critical network of -∇ 2 ρ (charge concentration) or ∇ 2 ρ (charge depletion). An example for the VSCC graph of a water molecule is shown in Fig. .f Fig. of ). This VSCC graph can clearly be seen to connect the lone pairs either side of the oxygen atom. This behaviour is reflected in the critical network of the 90% ELF isosurface (Fig. , middle), where the lone pairs can be very clearly seen as lobes aligned along the perpendicular direction to the bonds. Such charge concentration arises from distortions in the valence shell of the oxygen atom due to the hydrogen atoms, which can be seen by looking at the maxima families of |∇ 2 ρ(r)| (Fig. , bottom, valence shells are shown in blue, c.f the shells of Ne in Fig. ) -note that core shells (pink, for example) retain their spherical nature.