Disodium helide

Disodium helide (Na₂He) is a compound predicted to form when sodium and helium are compressed to extreme pressures. Its helium atoms occupy lattice sites while electron pairs localize in cavities, giving it electride character.

Connect

Electride: A solid in which electrons occupy cavities or channels and act as anions. Na₂He belongs to this class because its localized electrons occupy lattice cavities.
First-principles calculation: A computational method that predicts material properties from quantum mechanics without fitted empirical parameters. Such calculations identified Na₂He’s stability and unusual electronic structure.
Diamond anvil cell: A device that compresses tiny samples between opposing diamond tips to reach extreme pressures. It provides a possible route to pressures needed to investigate Na₂He experimentally.
Noble gas: An element in Group 18, generally characterized by a filled valence shell and low chemical reactivity. Helium’s conventional noble-gas behavior contrasts with its inclusion in Na₂He.
Electron localization: The confinement of electrons to particular regions rather than their delocalization across a material. Extreme compression confines Na₂He electrons between sodium atoms.
Crystal structure prediction: Computational methods for finding stable crystal arrangements from chemical composition and physical conditions. Structure searches revealed a stable Na₂He arrangement at high pressure.
Synchrotron X-ray diffraction: A structural analysis method that uses intense synchrotron X-rays to measure diffraction from materials. Diffraction could test whether compressed sodium and helium form the predicted lattice.
Helium compounds: Chemical substances containing helium, including species formed under extreme conditions or in specialized environments. Na₂He is a solid-state example among rare forms of helium chemistry.
Crystal structure: The ordered arrangement of atoms, ions, or molecules in a crystalline solid. Na₂He’s lattice places helium atoms and electron-filled cavities in distinct sites.
Evolutionary algorithm: An optimization method that searches by iteratively selecting and modifying candidate solutions. Evolutionary searches helped locate candidate structures for compressed sodium–helium mixtures.