Crystal structure of gallium metal

The crystal structure of Ga is too complex for one to attempt to `derive' it theoretically in any meaningful sense. However, one can test that the observed structure `makes sense' from various points of view. We find that it does, as regards number of near neighbours, their distances, covalency and the axial ratios which make Ga pseudohexagonal about the a axis as well as pseudotetragonal about the c axis. Our considerations are based on the expression for the total energy in terms of the pseudopotential v(q) . The situation is dominated by the position of q 0 where v(q) passes through zero and by several sets of Brillouin zone planes which just envelope the Fermi sphere. The band gaps across the latter immediately explain qualitatively the marked anisotropy of the resistivity tensor. The distance of the first minimum in the interatomic potential favours a structure with about seven nearest neighbours. Covalency amounts to about 27 kcal (g-atom) -1 .