Computationally Designed Crystal Structures of the Supertetrahedral Ga₄C and Ga₄Si Solids

The structural, mechanical, electrical, and optical properties of new supertetrahedral structures cF-Ga₄X (X = C, Si) were studied by using a solid state DFT calculation. The crystal structures of cF-Ga₄X are built based on a diamond crystal lattice, in which pairs of adjacent carbon atoms are replaced by Ga₄X fragments, where Ga₄ is a tetrahedron of gallium atoms. Calculations have shown that new mixed-type supertetrahedral structures are dynamically stable, have densities of 3.49 g/cm³ (X = C) and 2.65 g/cm³ (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.