Overview

Sunny is a Julia package for modeling atomic-scale magnetism. It provides powerful tools to study equilibrium and non-equilibrium magnetic phenomena. In particular, it allows estimation of dynamical structure factor intensities, $\mathcal{S}(𝐪,ω)$, to support quantitative modeling of experimental scattering data.

Features include:

• Generalized spin dynamics using SU(N) coherent states.
• Ability to specify a crystal from a .cif file or its spacegroup symmetry.
• Interactive visualizations of the 3D crystals and magnetic ordering.
• 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, and optimization tools.
• Measurements of dynamical correlations. At low temperature, one can use linear spin wave theory and its multi-boson generalization. This generalizes to finite temperatures using the classical dynamics, which allows for strongly nonlinear effects.
• Long-range dipole-dipole interactions accelerated with the fast Fourier transform (FFT).
• Support for comparison with experimental data: form factor, dipole factor, temperature-dependent classical-to-quantum factors, intensity binning, etc.