Alloy Phase Diagrams From First Principles
The first applications of density-functional theory to disordered systems are described. The usual difficulty of solving the single-particle Schrödinger equation for systems lacking long-range order is circumvented by using the cluster-expansion method of Sanchez and deFontaine to describe the alloy, and deducing the coefficients appearing in this expansion from energy-band calculations for several ordered compounds. The cluster expansion obtained in this way describes the alloy as a continuous function of stoichiometry, short-range order and volume. We have used the technique, in combination with an approximate description of the entropy of mixing, to calculate the dominant features of the phase diagrams of 28 transition-metal alloy systems. Agreement with measured phase diagrams is generally very good. Not tested in these first applications of the technique is its ability to describe properties of disordered systems other than the total energy, properties such as the state density. Also not yet tested is the ability of the technique to directly predict the degree of short-range order present in the system, by minimization of the free energy.
KeywordsEntropy Librium CuAu
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