Na2He: a stable compound of helium and sodium at high pressure.

A CIF created from the information given in the caption to Figure 2, reproduced here Figure 2 | Crystal structure of Na2He at 300 GPa. a,b, Ball-and-stick representation (a, pink and grey atoms represent Na and He, respectively) and polyhedral representation (b), where half of the Na8 cubes are occupied by He atoms (shown as polyhedra) and half by 2e (shown as red spheres). c, Electron localization function (ELF, which measures the spatial localization of electrons) plotted in the [110] plane at 300 GPa. This structure has space group Fm-3m with lattice parameter a = 3.95 Ã at 300 GPa and Na atoms occupying the Wyckoff position 8c (0.25,0.25,0.25) and He atoms occupying the 4a (0,0,0) position.