  Electron correlation effects in the half-metallic ferromagnet NiMnSb are
investigated within a combined density functional and many-body approach.
Starting from a realistic multi-orbital Hubbard-model including Mn and Ni-d
orbitals, the many-body problem is addressed via the Variational Cluster
Approach. The density of states obtained in the calculation shows a strong
spectral weight transfer towards the Fermi level in the occupied conducting
majority spin channel with respect to the uncorrelated case, as well as states
with vanishing quasiparticle weight in the minority spin gap. Although the two
features produce competing effects, the overall outcome is a strong reduction
of the spin polarisation at the Fermi level with respect to the uncorrelated
case. This result emphasizes the importance of correlation in this material.
