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.