A New Approach to Noncollinear Spin Density Functional Theory beyond the Local Density Approximation

The application of density functional theory to heavy elements and magnetic materials requires the generalization of existing functionals to the case of noncollinear spins. This letter describes a new idea to achieve such a generalization which, unlike previous efforts in this direction, (i) affords a nonvanishing local magnetic torque, (ii) is invariant with respect to spin-rotations, (iii) is free from numerical instabilities in regions of small magnetization, and (iv) reduces to the proper collinear limit.