Tutorial 3. Numerical Tools for Modeling Spin Dynamics

ANCILLARYEVENT · MAR-3T · ID: MAR-3T

Modeling spin dynamics for spectroscopy poses significant challenges due to the need to accurately capture quantum fluctuations, multi-spin correlations, and anisotropic exchange interactions that govern the magnetic excitations in real materials. Traditional methods, such as linear spin-wave theory, often fail for materials that behave semi-classically but require a treatment beyond the standard 1/S expansion. Exact quantum approaches, such as exact diagonalization, Density Matrix Renormalization group (DMRG) or quantum Monte Carlo (QMC), are severely limited by system size and the sign problem, making them unsuitable for modeling many realistic materials under experimental conditions. 

Recent developments in semi-classical methods have provided a powerful alternative. In particular, the Sunny package has emerged as a state-of-the-art tool that extends classical spin dynamics by incorporating quantum fluctuations through a generalization of the large-S expansion. This approach enables the simulation of realistic spin Hamiltonians, including anisotropic and long-range interactions, over large system sizes and time scales, allowing direct computation of dynamical structure factors and other spectroscopic observables. Such advances are bridging the gap between theory and experiment, making it possible to model complex magnetic materials with unprecedented accuracy.

The proposed tutorial includes four lectures that will introduce the audience to Sunny.

Topics:

• Introduction to inelastic scattering probes and challenges faced with modeling data. 
• Semi-classical methods for modelling spin dynamics.
• Introduction to the Sunny platform.
• Hands on tutorial.