Given a target function value f iso , an isosurface of f can be defined as {x ∈ R N : f (x) = f iso }. Due to the delocalized nature of electrons in molecules, isosurfaces are commonly used in molecular visualization. The ability to identify families of maxima allows the topological analysis of such isosurfaces by defining an auxiliary function f I (x) = exp(-|f (x) -f iso |) which will be maximal where f (x) = f iso . The maxima family (or families) where f I (x) ≈ 0 then serve as a suitable definition of isosurfaces. An example of this can be seen in Fig. , where non-covalent bonding in H 2 under a strong magnetic field (as explored in ) can be identified as the separation of the half-maximum-value isosurface of the electron density (where ρ(x) = max(ρ)/2) into two distinct maxima families.