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, Cu 3 Au, and CuAu 3 , including the sequence of transitions from the disordered to the modulated CuAuII phase to the low-temperature CuAu I phase