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.