Sunny, a user-friendly Julia package for simulating generalized spin dynamics

We illustrate the Sunny software package for simulating magnetic materials (https://github.com/SunnySuite/Sunny.jl). Sunny can simulate the classical Landau-Lifshitz spin dynamics, as well its recent generalization to a theory of SU(N) coherent states, whereby each quantum spin is described as N complex amplitudes that evolve dynamically under a nonlinear Schrödinger equation. Quantization of the classical theory at low temperatures yields linear spin wave theory, or its multi-boson generalization which captures multipolar excitations. The resulting dynamical correlations can be compared with experimental scattering data, e.g. neutrons or xrays. A particularly useful feature of Sunny is its support for analyzing the space group symmetries of a crystal, and using them to constrain the space of allowed spin Hamiltonians. This talk will demonstrate various features of Sunny through examples. In particular, we will show an example of a nonequilibrium dynamical quench that leads to the formation of a liquid of CP² skyrmions.