Exchange-correlation functionals for noncollinear spin density functional theory

We present new semilocal exchange and correlation energy functionals for spin density functional theory (SDFT). These exchange and correlation functionals are directly derived for noncollinear magnetism, in order to preserve gauge invariance, and give rise to non-vanishing exchange correlation torques. We further propose generalization of self-interaction corrections to the non-collinear case, which also give rise to non-vanishing exchange-correlation torques. These functionals are tested for frustrated antiferromagnetic clusters and are shown to perform favorably compared to the far more expensive optimized effective potential for exact exchange. This provides a path forward for functional development in noncollinear SDFT and the ab initio study of magnetic materials in and out of equilibrium.