The radius of an atom in covalent compounds

An empty-core pseudopotential to account for the atomic core and a linearized Fermi-Thomas equation to describe the valence electrons has been formulated previously to treat the simple metals. The covalent bond in semi-conductors is considered in the present work and the Dirac-Fermi-Thomas equation is used to describe the valence electrons. Calculations of the nearest-neighbor distance in fifteen AB covalent compounds with tetrahedral coordination were carried out and it was found that deviations from the experimental values correlate with the ionicity scale defined by Phillips.