The vacancy formation and migration enthalpies $H_f$ and $H_m$ in tantalum are calculated by means of ab initio pseudopotential techniques. The results obtained after relaxation with supercells containing 54 atomic sites ${(H}_f=3.0\mathrm{}$ eV and $H_m=0.8\mathrm{}$ eV) are in excellent agreement with experiments ${(H}_f=3.1\mathrm{}$ eV and $H_m=0.7\mathrm{}$ eV). The electronic entropy has a moderate influence on 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 tracer self-diffusion coefficient is well reproduced within the rate theory using an estimate of the vibrational formation entropy and the attempt frequency.

• Received 19 April 1999

DOI:https://doi.org/10.1103/PhysRevB.60.7001