Sunny.jl

Sunny is a package for simulating classical spin systems, including the Landau-Lifshitz dynamics of spin dipoles and its generalization to multipolar spin components. The latter is especially powerful for modeling magnetic compounds with strong single-ion anisotropy interactions.

Sunny provides the following features:

• Generalized spin dynamics using SU(N) coherent states.
• Ability specify a crystal by a .cif file, or using its spacegroup symmetry.
• Symmetry analysis to classify allowed interaction terms, and to propagate them by symmetry.
• Single-ion anisotropy at arbitrary order, which can be specified using Stevens operators or as a polynomial of spin operators.
• Monte Carlo sampling of spin configurations in thermal equilibrium.
• Ewald summation for long-range dipole-dipole interactions, accelerated with the fast Fourier transform (FFT).
• Estimation of the $\mathcal{S}(\mathbf{q}, \omega)$ dynamical structure factor data, with options for various corrections (form factor, classical-to-quantum factors, ...)

Work in progress includes:

• Linear spin wave theory and its generalization to SU(N) coherent states.
• Interactive visualizations of the 3D crystals and structure factor data.
• MPI-distributed Monte Carlo sampling, including parallel tempering.