The electron density and bonding in beryllium metal as studied by Fourier methods

The bonding in Be metal is studied by calculation of valence and deformation density maps from data collected by Brown [Philos. Mag. (1972), 26, 1377-1394]. The deformation maps show clearly that the predominant interaction is bonding through the tetrahedral holes of the h.c.p. lattice. The valence-density maps generally agree with least-squares-model maps published by Stewart [Acta Cryst. (1977), A33, 33-38], though differences in detail exist which may result from incomplete space filling of the least-squares model functions. The experimental densities are interpreted in terms of the hybrid-orbital model of Altmann, Coulson & Hume-Rothery [Proc. R. Soc. London Ser. A, (1957), 240, 145-155] as corresponding to (sp²)^a (sp)^b hybridization of the Be atoms with b > a. Agreement with a theoretical density obtained by the augmented plane wave calculation of lnoue & Yamashita [J. Phys. Soc. Jpn. (1973), 35, 677-683] supports both theoretical and experimental procedures.