Fig. 4: Band structure of cubic helium.

The energies are aligned to the Fermi energy. a White lines are the bands resulting from the direct approximation, where the energies results at all k-points equal those at k₀. b Connector result, plain (intensity plot) and constrained (blue dots), following the prescription in the text. c Comparison of first principles results (red line) with constrained connector (blue dots). In white, HEG folded into the Brillouin zone of helium and attached to the second band at Γ. For comparison of the lowest band, which corresponds to a localized state, the lowest HEG band is used.