Ionicity of bonding in elemental solids

Elemental solids are categorized into four classes based on the occupation of Wyckoff positions (WPs), to investigated their ionicities. In class I of elemental solids with only one WP occupied, such as diamond, the ionicities of all bonds are zero. In the other three classes of elemental solids with multiple equivalent or inequivalent WPs occupied, charge transfer can exist between atoms occupying different WPs, and hence have an ionic character. We identify some previously unrecognized elemental solids with partial ionicities using the method of Bader charge analysis. Especially, charge transfer in a boron-rich phase (epsilon-B) is comparable with that in oxides.