PHASE-DIAGRAM CALCULATIONS FROM FIRST-PRINCIPLES

A unified approach to the study of alloys, using the Korringa-Kohn-Ros toker (KKR) formulation based on atomic sphere approximation (ASA) and coherent-potential approximation (CPA), which allows the treatment of the disordered alloys and ordered alloys on an equal footing is prese nted. Some of the improvements afforded by the present approach over o ther methods for calculating the electronic structure of alloys are th e following: (i) It allows the calculations of total energies, equilib rium lattice parameters, and other quantities for both the disordered alloys and selected ordered structures, since in either case the treat ment of the Hamiltonian within CPA is the same. (ii) It allows incorpo ration of charge-transfer effects, for instance, by varying the volume of the atomic sphere associated with each species in the alloy so tha t each atom is individually charge neutral. (iii) It allows, for the f irst time, the calculations of non-spherical charge density of the dis ordered alloys. In conjunction with the generalized perturbation metho d (GPM) in the ASA, the present approach provides an accurate and reli able way of studying phase stability and ordering tendencies of alloys at T = 0K. The effective cluster interactions obtained from the GPM m ethod can then be used in the cluster variation method for calculating the phase diagrams of alloys from first-principles.