On the other hand, |V(r)|/G(r) also increases by decompressing from 25 GPa (therefore, reentering in the stability-pressure regime of bcc). Calculating the projected density of states (pDOS) at variable pressures (15, 25 and 40 GPa, See Figure ), we can see that upon decompression the d-states become less and less dominant, while the s-state increase both in dispersion and magnitude. Therefore, we could interpret the results of Figure and Figure as a change in the spd-hybridization, where at lower pressures, the 4scharacter, more diffuse than the 3d orbitals, is dominant, since it better overlaps at longer distances; while at higher pressures (shorter distances), the 3d-character becomes the dominant one, and stronger thanks to its higher degree of localization. The decrease of the 4s-dispersion upon compression is probably a consequence of the increased localization of charge density at the center of the cell, since broadened and diffuse bands are more characteristics of metallic states. Moreover, the Pauli repulsion between two neighboring 4s-4s orbitals and the closer contact between 4s-components having different phase might also affect the s-states at higher pressures. A similar effect has also been observed in pressurized Li and Li(NH3)4 . Since Ca-sc is experimentally observed only at P > 30 -35 GPa, our topological analysis suggests that the stability of this phase of calcium is strictly connected to the overlap-ability of the 3d orbitals. To be noted, if Ca-sc is decompressed below 10 GPa, the NNA and the electride state disappear.