Computationally Designed Crystal Structures of the Supertetrahedral Al₄X (X = B, C, Al, Si) Solids

New metastable crystalline forms of the supertetrahedral Al₄X (X = B, C, Al, Si) solids have been computationally designed using density functional theory calculations with imposing of periodic boundary conditions. The geometric and electronic structures of the predicted new systems were calculated on the basis of the diamond lattice in which all carbon atoms are replaced by the Al₄X structural units, where X is boron, carbon, aluminum, and silicon atoms. The calculations showed that the dynamic stability of the Al₄X crystal structures critically depends on the nature of the bridging atom X: supertetrahedral Al₄C and Al₄Si solids are dynamically stable, whereas Al₄B and Al₄Al ones are unstable.