Obstructed atomic insulator inorganic electrides

To date, 1788 obstructed atomic insulators (OAIs) characterized by charge centers not localized at atomic positions have been identified. However, only a small fraction qualify as insulating inorganic electrides (IEs), making this subclass---OAI IEs---a largely unexplored territory in materials science. Herein, through an unconventional screening approach, we uncover 33 such OAI IEs from the full OAI dataset, including six electrically neutral and seven negatively charged candidates, fundamentally challenging the longstanding view that IEs are intrinsically electron rich in nature. Moreover, the synergistic effect between the electronegativity difference of cations and anions, bond lengths, and the size of interstitial positions determines the presence of interstitial anion electrons in OAI IEs. Unlike previously reported metallic IEs, the insulating nature of the OAI IEs enables the emergence of multidimensional boundary phenomena, including coexisting surface and hinge states. We identify 22 candidates that host a low work function $[\mathrm{\ensuremath{\Phi}}(\mathrm{WF})<4 \mathrm{eV}]$, a feature that markedly boosts the efficiency of ammonia synthesis. These results involve the screening, investigation, and application of insulating IEs, effectively linking the potential of insulating IEs to fields such as topological quantum chemistry, boundary engineering, and energy research.