Topological analysis of electron densities (viz. QTAIM) also offers a way of defining atoms within molecules. Within QTAIM, atoms are identified with basins (Figures and), non-overlapping regions of space within which all gradient trajectories of the electron density terminate at the same local maximum (i.e., a 𝜅 = -3 critical point). Note, therefore, that basins need not strictly be centered around nuclei but can be associated with NNAs. Neighboring basins are separated by zero-flux surfaces where ∇𝜌(𝒓) • 𝒏 = 0, and where 𝒏 is the normal to the surface at 𝒓. We will use such basins to ascribe partial charge to atoms inside molecules, and we suggest such measures, along with 𝜌 and ∇ $ 𝜌 at BCPs, as examples of potent density-based quantum computational fidelity witnesses.