Critical points are labelled using two symbols, (ω, σ), where the value of the first is related to the size of the space (e.g. In Ca-bcc at 25 GPa, a NNM is yet to be found, but this phase presents two bond cps (saddle points characterised by two negative and one positive curvature, (3,-1)) instead. One of these is located at the tetrahedral site (ELF = 0.62), and one is located at the octahedral site (ELF = 0.59). Though the ELF values are smaller than for the ELF blob (corresponding to a minimum in the electron density) found in the fcc phase, the electron density is higher, and the overall Laplacian is negative. Ca-sc at 40 GPa, instead, possess both a NNM, which integrates a total of 0.63 electrons in its basin, 100 a negative Laplacian of the electron density, and an ELF value close to 1 at the cp location (0.94). Therefore, according to the criteria proposed in Sec. , only Ca-sc could be considered as an electride. As we mentioned earlier, Ca-sc is metallic, although characterized by a pseudo-gap. Therefore, it is still debatable whether the presence of a finite band-gap is needed to identify an electride in the solid state.