Electron correlation and electron-lattice interactions are two fundamental aspects of condensed-matter physics, which, combined with nonbound interstitial anionic electrons, can give rise to abundant physical phenomena. In this work, we combined crystal structure prediction with first-principles calculations to explore alkaline-earth halides as potential hosts of exotic electrides and physical properties. We identified nine unconventional stoichiometric phases, among which four exhibit pronounced electride characteristics. In particular, the $P\text{−}6m2$ CaI phase adopts a hexagonal structure, where interstitial electrons are localized within the calcium honeycomb layers. The strong interstitial-electron correlations drive a Mott metal-insulator transition, with an antiferromagnetic ground state. For the ${\mathrm{Ca}}_3\mathrm{I}$ compound, strong interactions between interstitial electrons and adjacent calcium lattices promote a structural transformation from the $P{6}_3/mmc$ to the Cmcm phase, accompanied by the emergence of superconductivity with a transition temperature of 7.1 K at 70 GPa. Moreover, a metastable $P4/mmm {\mathrm{Ca}}_3\mathrm{I}$ electride is also predicted to exhibit superconductivity with a transition temperature of approximately 6.9 K. These findings highlight that interstitial electrons located near the Fermi level can induce strong electron correlations and enhance electron-phonon coupling, thereby giving rise to a rich spectrum of physical behaviors, including superconductivity and magnetism.

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• Crystal structure
• Electronic structure
• High-pressure studies
• Magnetism
• Superconductivity
• Antiferromagnets
• Mott insulators
• Superconductors
• BCS theory
• Density functional theory
• First-principles calculations