  The remarkable mechanical properties of high entropy alloys can be further
improved by interstitial alloying. In this work we employ density functional
theory calculations to study the solution energies of dilute carbon
interstitial atoms in tetrahedral and octahedral sites in bcc HfNbTiVZr. Our
results indicate that carbon interstitials in tetrahedral sites are unstable,
and the preferred octahedral sites present a large spread in the energy of
solution. The inclusion of carbon interstitials induces large structural
relaxations with long-range effects. The effect of local chemical environment
on the energy of solution is investigated by performing a local cluster
expansion including studies of its correlation with the carbon atomic Voronoi
volume. However, the spread in solution energetics can not be explained with a
local environment analysis only pointing towards a complex, long-range
influence of interstitial carbon in this alloy.
