Constrained density functional theory for first principles spin dynamics

Constrained density functional theory is used to formulate a theory of general noncollinear spin systems which makes it possible to implement first principles spin dynamics in a manner that is firmly grounded in density functional theory. At each time step, local constraining fields are calculated from a self-consistent algorithm. In addition to discussing the conceptual basis of the resulting constrained local moment model we illustrate the theory by explicit calculations for the relative rotation of the corner and body center moments of bcc iron.