Dynamical exchange interaction from time-dependent spin density functional theory

Abstract

We report on ab initio time-dependent spin-dynamics simulations for a two-center magnetic molecular complex within the framework of the time-dependent noncollinear spin-density functional theory. In particular, we discuss how the dynamical behavior of the ab initio spin-density in the time domain can be mapped onto a model Hamiltonian based on the classical Heisenberg spin-spin interaction JS1?S2. By analyzing individual localized-spin trajectories, extracted from the spin-density evolution, we demonstrate a practical method for evaluating the effective Heisenberg exchange coupling constant J from first-principles simulations. We find that J, extracted in such a dynamical way, agrees quantitatively with that calculated by the standard density functional theory broken-symmetry scheme.