  We present a novel functional for spin density functional theory aiming at
the description of non-collinear magnetic structures. The construction of the
functional employs the spin-spiral-wave state of the uniform electron gas as
reference system. We show that the functional depends on transverse gradients
of the spin magnetization, i.e., in contrast to the widely used local spin
density approximation, the functional is sensitive to local changes of the
direction of the spin magnetization. As a consequence the exchange-correlation
magnetic field is not parallel to the spin magnetization and a local
spin-torque is present in the ground state of the Kohn-Sham system. As a
proof-of-principle we apply the functional to a Chromium mono-layer in the
non-collinear ${120^{\circ}}$-N{\'e}el state.
