Instead, the ratio defined as |V(r)|/G(r), is more useful to characterize the type of interaction and highlight variations in the local energies . A ratio |V(r)|/G(r) < 1 corresponds to a pure closed-shell interaction region, while |V(r)|/G(r) > 2 is associated to a pure shared-shell interaction region (1 < |V(r)|/G(r) < 2 is the intermediate region) . Therefore, the NNM in Ca-sc corresponding to the center of the Ca8 interaction is topologically characterized as a sharedshell, since |V(r)|/G(r) > 2, which is in line with ours and previous Wannier-function analyses , and overall, the MCB model. Moreover, |V(r)|/G(r) is calculated to increase above 25 GPa, showing that, despite the fact that the total charge Q in the basin decreases, the overlap between the spdhybrid orbitals of Ca8 increases.