Superatomic Hydrogen: Electron Delocalization at Reduced Pressures Compared to Metallic Hydrogen

ABSTRACT Realizing metallic hydrogen, a crystal state in which hydrogen atoms exhibit electron delocalization due to high‐density aggregation, has long been a central goal in high‐pressure condensed matter physics. However, the extreme pressures required—exceeding hundreds of gigapascals—remain a formidable challenge. Here, we report a discovery that a finite number of hydrogen atoms can exhibit electron delocalization similar to that in metallic hydrogen crystals when compressed under non‐periodic symmetry. Of particular importance, high‐precision ab initio calculations indicate that hydrogen atoms in this state not only correspond to high density, but also requires pressures approximately two orders of magnitude lower than those for metallic hydrogen. We refer to these high‐density hydrogen atom aggregates that differ from metallic hydrogen but also exhibit electron delocalization as superatomic hydrogen. Atomic‐level analyses reveal that, in superatomic hydrogen, the electron density associated with the central hydrogen atom is redistributed and all electrons are delocalized over superatomic molecular orbitals, effectively matching the recognized properties of metallic hydrogen. Thus, our discovery establishes a superatomic framework for understanding high‐density hydrogen aggregation, opening different avenues for fundamental research on elemental hydrogen under confinement.