GW study of the half metallic band gap of zinc blende CrAs

We determined the semiconducting gap of zinc blende (ZB) CrAs within the $GW$ approximation ($GW$A). This is the first $GW$ calculation of a half-metal. Previous calculations using density functional theory within the generalized gradient approximation (GGA) determined a gap of 1.8 eV, but the GGA is known to give too small of a value for this quantity in semiconductors. Additionally, since ZB CrAs is a half metal, one of its spin channels behaves like a metal and changes the quasiparticle screening compared to the insulating case. Due to the local field effect, we only included the $\Gamma$-point term in the metallic channel calculation of the polarizability while keeping the full set of terms in the insulating channel $GW$ calculation. Preliminary results suggest these terms from the polarizability produce little change in the value of the semiconducting gap when compared to the ``full'' $GW$A calculation.