Electronic structure calculations of vacancy parameters in transition metals: Impact on the bcc self-diffusion anomaly

The group dependence, i.e., the variation with the number of d valence electrons, of vacancy parameters in transition metals with the body-centered cubic (bcc) structure is investigated via a combination of electronic structure calculation techniques. A semiempirical tight-binding d-band approach is proposed that shows that the position of the Fermi level with respect to the pseudogap governs the sharp variations along a transition metal series of (i) the formation energy, (ii) the relaxation energy, (iii) the migration energy, and (iv) the electronic contribution to the formation and migration entropies. These predicted trends are confirmed by first-principles calculations in 5d bcc metals (bcc-Hf, Ta, and W) including structural relaxations within plane-wave pseudopotential computations performed on supercells containing up to 54 sites. The agreement with available experimental data is very conclusive. A fast version of the full potential linear muffin-tin orbital method is then used to show the weak influence of the method within density functional theory in the local density approximation and to generalize these results—without relaxation—to the 3d and 4d series. This data base allows us to test the validity for vacancy studies of spd tight-binding models proposed in the literature. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 927–939, 2000