  We have computed the variation of the vacancy formation energy with pressure
for Ta. Total energy calculations were performed for 16 and 54 atom supercells
using a mixed basis pseudopotential method which uses pseudo-atomic orbitals
and low energy plane waves as the basis set, within density functional theory
(LDA and GGA). The vacancy formation energy is found to increase from 2.95 eV
at ambient pressures to 6.96 eV at 300 GPa, and the vacancy formation volume
decreases from being 53.4% of the bulk volume per atom at ambient pressure to
19.6% at 300 GPa, for a 54 atom supercell. The structural relaxation energy is
found to increase with pressure from 14% of the vacancy formation energy at
ambient pressure to 16% at 300 GPa.
