The analysis of ''empty space'' in the PdGa5 structure

The structure of PdGa5 is characterized by a framework of condensed bicapped tetragonal antiprisms [PdGa10]. The appropriate symmetry governed periodic nodal surface (PNS) divides the space into two labyrinths, The atoms of the coordination polyhedra are located in one labyrinth or are close to the surface. The second labyrinth seems to be ''empty''. The electron localization function (ELF) calculated by the TB-LMTO method, shows that the ''empty'' labyrinth contains the regions with high ELF values. These regions are related to inter-polyhedral Ga-Ga bonds forming Ga-4 squares. The vertices of eight covalently bonded Ga-4 squares build tetragonal antiprisms which are centered by Pd atoms. High electron density but tow ELF values inside these coordination polyhedra of Pd represent regions of delocalized (metal-like) electrons. Thus, the PNS separates the regions of different bonding character. Some relations to stuffed derivatives of the PdGa5 structure are discussed.