The vacancy formation and migration enthalpies H-f and H-m in tantalum are
calculated by means of ab initio pseudopotential techniques. The results ob
tained after relaxation with supercells containing 54 atomic sites (H-f = 3
.0 eV and H-m = 0.8 eV) are in excellent agreement with experiments (H-f =
3.1 eV and H-m = 0.7 eV). The electronic entropy has a moderate influence o
n their temperature dependence. The effects of structural relaxation, which
reduce H-f by 14%, are significantly larger than for group-VI elements and
are typical of a normal behavior for the bcc structure. The experimental t
racer self-diffusion coefficient is well reproduced within the rate theory
using an estimate of the vibrational formation entropy and the attempt freq
uency. [S0163-1829(99)12133-7].