The electron density of a chemical system, ρ(r), is a quantum mechanical observable that can be either probed with X-ray diffraction experiments or calculated with ab-initio methods . This scalar function gathers quantitative information on chemical bonding and atomic properties, which can be extracted with the QTAIM . Even though chemical bonding has no quantum mechanical definition, retrieving chemical properties from an experimental (fully relativistic and fully correlated) electron density , not approximated by levels of theory, can become very useful to verify theoretical models and elucidate the physical nature of crystalline materials.