However, in absence of high-quality diffraction data, performing an analogous topological survey on the theoretical electron density can still be helpful to rationalize chemical behavior, and perhaps, to guide future experiments. Therefore, we present here (Figure ) the topological analysis of the electron density of Ca-sc as a function of pressure (from 15 to 40 GPa), together with its electron localization function (ELF). The study of these two quantities (ρ(r) and ELF) is becoming the gold standard to characterize possible HPEs . Before proceeding with our analysis, we must clarify that pure Ca-sc is not observed at P < 35 GPa , and that computationally, we predict this phase to become thermodynamically preferred over bcc and fcc only above 26 GPa (Figure ). However, the computational exploration of a wider range of pressure for this phase, especially for longer Ca-Ca distances, might give useful insights to understand the type of interactions triggering the electride state.