Designing Molecular Electrides from Defective Unit Cells of Cubic Alkaline Earth Oxides

Electrides are an unusual class of compounds where electrons are localized in space distinct from atomic positions and behave like anions. This type of localization makes electron density very “flexible”, thus even a weak electric field causes significant polarization, that is, nonlinear optical properties. To date, all synthesized electrides are bulk compounds. However, molecular size electrides would have plenty of applications in nanoscience. It is known that cubic halide and oxide crystals possess anion vacancies which are occupied by electron pairs or single electrons. In this work, we propose a strategy for designing molecular electrides as defective unit cells of cubic crystals with a missing anion. We limit our study by the second group of the periodic table and explore the potential energy surface of X₄O₃ stoichiometry which corresponds to the defective cell of cubic XO crystal where X stands for Be, Mg, Ca, Sr, and Ba. Defective cell geometry becomes more dominant and nonlinear optical properties become more intense upon transition from lighter to heavier metal. The potential energy surface of Mg₄O₃, Ca₄O₃, Sr₄O₃, and Ba₄O₃ is very pure which makes them promising structures for synthesis.