THEORETICAL MODELING OF THE STRUCTURAL, THERMODYNAMIC, ELECTRONIC, AND MAGNETIC-PROPERTIES OF ALLOYS

In recent years, the theory of alloys has progressed on three different levels. On the first level, favoured by physicists, the properties of alloys are calculated by solving the Schrodinger equation in the local-spin-density (LSD) approximation. Given the high accuracy that is required, such calculations can be performed only for systems with a maximum of hundred nonequivalent atomic sites, even on the most powerful computers. On the second level, chemists describe bonding in terms of the sigma, pi and delta transfer integrals resulting from the angular-dependent valence orbitals. Chemical intuition allows to introduce simplifications, and at the reduced accuracy of a Tight-Binding-Huckel equation, systems with up to a few thousand atoms may be modelled quite successfully. The third level corresponds to the reasoning traditional in metallurgy: atoms are considered as soft spheres interacting through pair - or embedded-atom potentials. The simplicity of the interatomic force law allows to simulate the properties of ensembles with up to a hundred thousand atoms. Progress on all three levels will be illustrated at the example of crystalline and liquid Zintl phases, of crystalline and amorphous magnetic alloys, and of quasicrystalline alloys.