Emerging Electride Behavior and Metallization in Molecular Hydrogen under High Pressure

We demonstrate that the metallization of molecular hydrogen under pressure is accompanied by the emergence of an electride-like behavior, characterized by the localization of electrons in interstitial regions among H₂ molecules. This mechanism distinguishes H₂ from other molecular crystals, where metal-insulator transitions are typically driven by bond rearrangements. The presence of interstitial electrons may significantly influence the electron-phonon coupling and, consequently, the superconducting properties of molecular hydrogen. Importantly, these features persist in metal superhydrides stabilized at moderate pressures, where molecular units are retained. As a result, electride-like electronic states are an important factor in these compounds, which are among the most promising candidates for achieving high-T_c superconductivity under moderate pressures.