  We propose a powerful extension to combined molecular and spin dynamics that
fully captures the coupling between the atomic and spin subsystems via
spin-orbit interactions. Its foundation is the inclusion of the local magnetic
anisotropies that arise as a consequence of the lattice symmetry breaking due
to phonons or defects. We demonstrate that our extension enables the exchange
of angular momentum between the atomic and spin subsystems, which is critical
to the challenges arising in the study of fluctuations and non-equilibrium
processes in complex, natural, and engineered magnetic materials.
