Atomistic Landau theory of ordering and modulated phases in Cu-Au alloys

We present a Landau theory derived from an alloy Hamiltonian based on a quantum-mechanical description of cohesion in metallic systems. This Landau theory, obtained by making a mean-field approximation, provides an excellent description of the ordering transitions in CuAu, ${\mathrm{Cu}}_3$Au, and ${\mathrm{CuAu}}_3$, including the sequence of transitions from the disordered to the modulated CuAu II phase to the low-temperature CuAu I phase.