To summarize our earlier article , the field 𝒫 is constructed by mapping electron density gradient (∇𝜌) paths to points in 𝒫. The origin and terminus of a gradient path (G) are respectively a local minimum called a cage critical point (CP)-which may be at ∞-and a local maximum typically coincident with a nucleus and thus dubbed a nuclear CP. Each G is also parameterized by arclength (𝑠).