Approaches for the Computation of Magnetic Exchange Couplings.

Computation of magnetic exchange coupling constants is important for a growing number of areas, including spintronics, magnetic memory storage, and novel molecular magnet design. Determining exchange coupling for high-nuclearity complexes is not possible experimentally, and thus, computational methods are needed to make predictions. The most widely used methods compute the differences in total energies of a set of magnetic configurations, but the cost and difficulty increase steeply as more centers are added. Thus, it is desirable to have a black-box method that involves only a single state. Therein, we present new developments to compute magnetic exchange couplings based on approximate perturbation theory using a local rotation of the magnetization direction. This method can be implemented as an efficient post-processing tool, requiring only a single electronic structure calculation, and allowing automation to compute a large number of high-nuclearity complexes. We further compare results to related approximate Green's function method, which offers similar efficiency.