Torsion- and spin-density-functional theory for non-collinear magnetic systems

We present a torsion- and spin-density-functional theory by introducing torsion fields, which are produced by a spiral spin system, into the non-collinear magnetic system. Our approach extends the application of the spin-density-functional theory to the non-collinear magnetic systems. The new technique is demonstrated by the calculations of spin spiral ground state of γ-Fe employing the generalized gradient approximation; and we find the ground state at q=(2π/a)(0.15,0,1), which is in very good agreement with the experimental value.