One novel analysis tool contained in the work of Ciofini et al. is the idea to use the the second moments σ 2 elec and σ 2 hole [Eq. (5.11)] to introduce Gaussian approximations to ∆ρ elec (r) and ∆ρ hole (r). These provide quantitative realizations of the cartoons in Fig. , free of the nodal structure of the particle and hole densities and perhaps slightly easier to conceptualize. Examples are depicted in Fig. for a sequence of poly(p-phenyl)nitroaniline molecules. Due to the complex nodal structure along the conjugated backbone of these molecules, the barycenters of ∆ρ elec (r) and ∆ρ hole (r) are more clearly evident in their Gaussian approximations (Fig. ). Note also that whereas the particle and hole densities extend to the very edges of the molecule, the charge separation distance d - e-h (indicated by the blue arrows in Fig. ) is noticeably shorter. This is even more clear in the examples of Fig. , where plots of the particle and hole densities appear to be considerably more delocalized than the quantitative measure afforded by d - e-h . The extent of spatial charge separation is therefore smaller than plots of ∆ρ elec (r) and ∆ρ hole (r) might lead one to imagine. The latter are susceptible to the choice of isocontour value, which can sometimes be used to make a density appear almost arbitrarily compact or diffuse. For that reason, the author recommends that such plots should always indicate the fraction of the indicated density that is encapsulated within the isosurface, as in several of the figures presented elsewhere in this work.