Though we still do not have a predictive and general theory of why and when HPEs form, quantum chemical methods to identify them are available, though in many cases they have not been rigorously applied. In this section, we present a short overview, which is not meant to be exhaustive, of systems predicted to be HPEs, keeping in mind that in some cases further calculations would be required to confirm the classification. Na 2 He (Figure ) was synthesized at P > 113 GPa, 62 by putting sodium in a DAC loaded with helium and laser heating to T > 1500 K. In this system, the localized electrons sit in the interstitial pockets formed by the fluorite-type structure of Na 2 He. DFT-based topological analysis was performed at 200 GPa, confirming that the charge concentrations possessed a NNM (integrating a total of 1.022 electrons in its basin), negative Laplacian of the electron density at the NNM, and were characterized by ELF blobs with isovalue close to 1. At the GW level of theory, the band-gap of Na 2 He was found to be comparable to that of Na-hP 4 (1.8 eV at 200 GPa), suggesting it is also an insulating electride.