Ab Initio Molecular Dynamics Simulation of the Amorphous Structure of Ca-Mg-Cu and Ca-Mg-Zn Alloys

The atomic and electronic structures of several Ca-Mg-TM amorphous alloys (TM is Cu or Zn) have been analyzed using ab initio molecular dynamics simulation and neutron diffraction. Partial pair distribution functions have been produced and the pair bond distances and partial coordination numbers have been reported for these alloys. Similarities and differences in the amorphous structures of the Ca-Mg-Cu and Ca-Mg-Zn alloys have been discussed. Strong interactions between Ca-Cu, Mg-Cu and Ca-Zn atom pairs rooted from the orbital hybridization of the s-p-d electrons have been recognized to result in noticeable shortening of respective atom pair bond distances and pronounced chemical short range ordering near the TM atoms. Voronoi tessellation analysis has shown that the polytetrahedral-type clusters and five-coordinated atom pairs dominate in the amorphous structures, which indicates that tetrahedra and pentagonal bi-pyramids are the main building blocks in these amorphous alloys.