Rationalization of structures of binary alloys in a real space atomic level perspective

The understanding of the structure and bonding of intermetallic phases poses a unique challenge to theory. On one hand, first-principles calculations may be used to obtain accurate physical properties, on the other hand, the fundamental principles governing the observed structures is still unknown and often limited to simple models such as the Zintl concept or Meidema's rules. In this paper, a real space theoretical framework based on the analysis of the electronic density of states (DOS) in terms of its moments is proposed to bridge the gap between these two extremes. The moments of DOS are directly related to local structural motifs, thus allowing the identification of basic stabilizing structural features as a function of electron concentration. This approach is used to interpret the binary Al-Li phase diagram and the structural stability of high-pressure phases of K-Ag alloy. Since there is almost complete electron transfer from the alkali metal (Li and K) to Al and Ag in these alloys, the main factor governing the structural stability is the effective number of valence electrons on Al and Ag that directly determines the structural motifs. Thus, the structure, stability and phase boundary of alloy phases can be rationalized in a systematic manner. The principles developed here can be extended to make reliable predictions of the structure and stability of new intermetallic phases.