Points of Molecular Charge Distributions

The (3, -f 1) and (3, -h 3) critical points are associated with the presence of rings and cages respectively, just as the (3,-1) critical points are associated with the presence of chemical bonds which link the (3, — 3) local maxima at the positions of the nuclei. 

These qualitative associations of topological features of p with elements of molecular structure can be replaced with a complete theory, one which recovers all of the elements of structure in a manner that is totally independent of any information other than that contained within the charge density The underlying structure of the charge density is brought to the fore in its associated gradient vector field. The boundary condition of a quantum subsystem is also stated in terms of this field 

---