Towards a constrained local moment model for first principles spin dynamics

We argue that, as originally formulated, the first principles spin dynamics of the finite-temperature and non-equilibrium properties of itinerant magn ets recently proposed by Antropov el al. is not clearly defined within dens ity functional theory. We show how constrained density functional theory ca n be used to provide a formal basis for describing the instantaneous non-co llinear states that are being evolved according to the classical equation o f motion of spin-dynamics. We propose a constrained local moment (CLM) mode l in which specific orientational configurations are maintained by local tr ansverse constraining fields that are obtained self-consistently. A general algorithm for finding the constraining fields is used and the existence of a CLM state is demonstrated for specific model problems including a cell o f 512 Fe atoms for which the orientations of the magnetic moments are rando m.