Band theory of theCu3Au and CuAu3order-disorder transformations

A band theoretical model for the ${\mathrm{Cu}}_3$Au and Cu${\mathrm{Au}}_3$ order-disorder transformations is presented based on an extended cluster-Bethe-lattice method electronic theory and the cluster-variation configurational-entropy approximation. A single $s$-band tight-binding Hartree Hamiltonian is solved self-consistently for the electronic configurations of single atoms embedded in an effective medium in the presence of nearest-neighbor short-range-order correlations. The functional dependence of the ordering energy and the temperature dependences of long- and short-range order and internal energy are compared with the Ising theory and experimental data.