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

New metastable crystalline forms of the supertetrahedral AlX (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 AlX structural units, where X is boron, carbon, aluminum, and silicon atoms. The calculations showed that the dynamic stability of the AlX crystal structures critically depends on the nature of the bridging atom X: supertetrahedral AlC and AlSi solids are dynamically stable, whereas AlB and AlAl ones are unstable.