  Knowing the electronic structure of a material is essential in energy
applications to rationalize its performance and propose alternatives. Materials
for thermoelectric applications are generally small-gap semiconductors and
should have a high figure of merit ZT. Even if the Fe2VAl Heusler compound has
a decent ZT, its conductive nature (semi-metal or semiconductor) is not yet
clarified especially at low temperature. In this paper, we focus our DFT
calculations on the effect of temperature on the bandgap of Fe2VAl. In contrast
to what is usually observed, we show that both the temperature increase and the
formation of thermally-activated Al/V inversion defects (observed
experimentally), open the bandgap. Such an unusual behavior is the key for
reconciling all bandgap measurements performed on the Fe2VAl compound using a
standard GGA functional and could be an efficient way for improving the
thermoelectric properties of this family of materials.
