Trends in the Nearest-Neighbor Distance: Elements and Binary Compounds

Trends relating nearest-neighbor distance (d) in elemental materials and ANB^8-N compounds to atomic number (Z), valence (z), and principal quantum number (n) of the outermost filled electron shell are reported. These trends can be described by simple functional relationships which are typically accurate to within a few percent. For elements, these relations are dZ1/3nconstant for fixed z, and d1/nZ4/3(Z-z+12) for fixed n. An analysis of the results based on a Fermi-Thomas model for the core electrons and a free-electron model for the valence electrons is given. The trend observed for the ANB^8-N compounds is that dZ̄1/3n̄constant for a fixed cation species. This relation is used to construct a modified Mooser-Pearson plot which yields a complete separation of zinc-blende, wurtzite, and rocksalt structures.