Sunny, an open source code for simulating generalized spin dynamics

Sunny is an open source code to simulate the classical Landau-Lifshitz spin dynamics and its generalization to higher-order multipole moments. Like SpinW, this package provides symmetry analysis tools to facilitate the specification of model spin-Hamiltonians. Going beyond previous codes, Sunny also allows inclusion of arbitrary single-ion anisotropy terms. Strong anisotropy is readily induced through a combination of spin-orbit coupling and crystal field effects, and can have striking effects on observable phenomenology, e.g. in inelastic neutron scattering measurements. We present an overview of the features of Sunny, and illustrate how it can be used to simulate the dynamics of spin multipole fluctuations at arbitrary orders.