Computationally Designed Crystal Structures of the Supertetrahedral GaC and GaSi Solids.

The structural, mechanical, electrical, and optical properties of new supertetrahedral structures -GaX (X = C, Si) were studied by using a solid state DFT calculation. The crystal structures of -GaX are built based on a diamond crystal lattice, in which pairs of adjacent carbon atoms are replaced by GaX fragments, where Ga is a tetrahedron of gallium atoms. Calculations have shown that new mixed-type supertetrahedral structures are dynamically stable, have densities of 3.49 g/cm (X = C) and 2.65 g/cm (X = Si), and are narrow band gap semiconductors. From the performed molecular dynamics calculations, it follows that the homogeneous melting temperature of the gallium-carbon structure is in the range from 600 to 700 K and that of the gallium-silicon structure is in the range from 400 to 500 K.