Effect of Bardeen-Herring Correlation on Vacancy Diffusion in Anisotropic Crystals

From the Einstein relation, the principal diffusivities in anisotropic crystals are related to the atomic displacements. The effect of correlation is expressed in terms of correlation functions which are analogous to the correlation factor in isotropic diffusion. These correlation functions are calculated for vacancy self-diffusion in the primitive tetragonal, body-centered tetragonal, and hexagonal close-packed lattices by a computer technique. The possible use of correlation to determine mechanisms of anisotropic self-diffusion is discussed.