Predicted pressure-induced s-d electron transition of hydrogen in electride (Na2He)4H

Unexpected pressure-induced s-d electron transition had been observed in various s-block metals. However, it is noteworthy that no such transition has been reported for hydrogen, a unique element within the s block of the periodic table. Here, we propose using a zero-dimensional electride state, similar to a diamond anvil cell, to pressurize hydrogen under high pressure. The s-d electron transition of hydrogen was confirmed in our predicted electride (Na₂He)₄H at 200 GPa. The electride-state interstitial quasiatoms arranged themselves in a regular octahedral configuration centered at the hydrogen atom. This arrangement established a highly symmetrical Coulomb repulsion field, further compressing and triggering the central hydrogen atom to undergo an s-d transition. Additionally, our results indicate that the hydrogen doping results in the metallization and superconductivity of electride (Na₂He)₄H. The electride-state interstitial quasiatoms around hydrogen atoms dominate the superconductivity of (Na₂He)₄H. The presence of (Na₂He)₄H provides an example to confirm the promotion effect of the electride state on the superconductivity of electrides.