Quantum-mechanical origins of complex structures in Al-transition metal compounds

The energetic factors leading to the stability of complex structures in Al-rich transition-metal compounds are analyzed via ab-initio band-theoretic total-energy calculations comparing the Al12W and Cu3Au structures. For nearly half-filled d-bands, the Al12W structure is preferred by 1 eV per transition-metal atom or more. The preference for complex structures results from effects related to the shape of the d-projected electronic density of states, which are found to be more important than atomic-size effects, and are directly related to the complexity of the structure.