FORMATION ENERGY OF DISORDERED ALLOYS FROM THE ENERGETICS OF ORDERED COMPOUNDS

The cluster expansion technique is used in combination with first-prin ciples calculations of the total energy of ordered compounds to study the energetics of the disordered phase for a number of alloy systems. The effect of short-range order, as seen in the energy differences bet ween an alloy with the configuration corresponding to finite temperatu re and the perfectly random one is studied. The role of relaxation due to large size mismatch is discussed in terms of an effective cluster volume approximation. Very good agreement with measured energies of fo rmation is obtained when short-range order and relaxation effects are taken into account.