  First principles calculations have given a new insight into the energies of
point defects in many different materials, information which cannot be readily
obtained from experiment. Most such calculation are done at zero Kelvin, with
the assumption that finite temperature effects on defect energies and barriers
are small. In some materials, however, the stable crystal structre of interest
is mechanically unstable at 0K. In such cases, alternate approaches are needed.
Here we present results of first principles calculations of austenitic iron
using the VASP code. We determine an appropriate reference state for collinear
magnetism to be the antiferromagnetic double-layer (AFM-d) which is both stable
and lower in energy than other possible models for the low temperature limit of
paramagnetic fcc iron. We then consider the energetics of dissolving typical
alloying impurities (Ni, Cr) in the materials, and their interaction with point
defects typical of the irradiated environment. We show that using standard
methods there is a very strong dependence of calculated defect formation
energies on the reference state chosen. Furthermore, there is a correlation
between local free volume magnetism and energetics. The effect of
substitutional Ni and Cr on defect properties is weak, rarely more than tenths
of eV, so it is unlikely that small amounts of Ni and Cr will have a
significant effect on the radiation damage in austenitic iron at high
temperatures.
