PERTURBATION THEORY AND ALLOYING BEHAVIOUR .I. FORMALISM

The configuration-dependent part of the energy of a binary alloy may be expressed in terms of a single alloying potential, the difference between the two atomic pseudopotentials. Ordering can then be explained either in reciprocal space, or in real space using a single concentration-independent interionic potential. In real space the interaction between like atoms has the opposite sign to the interaction between unlike atoms. The total energy of an alloy may also be expressed in terms of the alloying potential alone, if the energy of the two components with the alloy crystal structure is known.