A new method was proposed for performing atomistic calculations, of point-defect entropies in metals, within the harmonic approximation to lattice vibrations. The principal problem was to predict accurately the defect formation entropy, in a macroscopic crystal, on the basis of atomistic calculations which were performed on a small system that contained relatively few atoms. The results of atomistic calculations could depend markedly upon the system size, geometry and boundary conditions. Two previously used methods (super-cell, embedded-cluster) were analyzed in 2 ways. First by using a linear elasticity model for a point defect, and then by atomistic calculations for a vacancy and an interstitial in Cu; using an embedded-atom potential. The results of the atomistic calculations confirmed the linear elasticity analysis and showed that the super-cell method was much more accurate than was the embedded-cluster method. The latter was nevertheless useful for calculating the defect core entropy; which happened to be a well-defined physical quantity. A new method was proposed, for defect-entropy calculations, which combined the embedded-cluster method and a quasi-continuum approximation beyond the cluster. This technique was called the elastically corrected embedded-cluster method, and had an accuracy which was comparable to that of the super-cell method; while extending defect-entropy calculations to larger system sizes.

Calculation of Point-Defect Entropy in Metals. Y.Mishin, M.R.Sorensen, A.F.Voter: Philosophical Magazine A, 2001, 81[11], 2591-612