A first-order perturbation treatment of XP-PCM allowed more in-depth studies of the compression of atomic orbitals. It was found that diffuse orbitals are being destabilized more significantly by pressure than core orbitals. Clearly, the spatial extension of an atomic orbital dictates how exposed its electrons are. A comprehensive XP-PCM study even presented data on the pressure-dependent electronic configurations of all atoms in the periodic table and allowed to establish a connection to magnetism under pressure. The XP-PCM data on electronic configurations ties in with DFT calculations using PBCs on lithium-beryllium alloys, in which the pressure-induced removal of two electrons from the lithium atoms was observed when the pressure was sufficiently high. The change in electronegativity with pressure has been studied extensively, since interpreting this quantity allows the rationalization of many chemical reactions. Confining potentials in combination with Hartree-Fock calculations, for example, have been used for investigating electronegativity under pressure. Using XP-PCM, an equation relating atomic radius and electronegativity has been developed. It was found that both decrease with increasing pressure. The same trend was recently found in a study using the helium compression chamber method investigating electronegativiy and chemical hardness under pressure. Additionally, XP-PCM allowed the calculation of electronegativity at shock fronts, and the related calculation of bond polarities and dissociation routes in energetic materials.