Sunny 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 specify a crystal by a .cif file, or using 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 correlation functions. For small supercells at low temperature, one can use linear spin wave theory and its multi-boson generalization. Alternatively, one can use the full classical dynamics to study systems with large supercells (e.g., disordered systems), or anharmonic effects with thermal fluctuations.
• Long-range dipole-dipole interactions accelerated with the fast Fourier transform (FFT).
• Various correction factors to facilitate comparison with experimental data (form factor, dipole factor, temperature-dependent classical-to-quantum factors, intensity binning, etc.).