Symplectic integrators for classical spin systems

TL;DR

This paper introduces a symplectic integrator for classical spin systems that preserves the phase space structure, enabling accurate long-term simulations of spin dynamics, including complex molecules.

Contribution

It develops a new symplectic integration method based on Hamiltonian decomposition and Lie-Trotter splitting for classical spin systems, broadening applicability.

Findings

Successfully applied to small spin systems and magnetic molecules

Preserves symplectic structure leading to stable long-term integration

Compared different order variants showing improved accuracy

Abstract

We suggest a numerical integration procedure for solving the equations of motion of certain classical spin systems which preserves the underlying symplectic structure of the phase space. Such symplectic integrators have been successfully utilized for other Hamiltonian systems, e. g. for molecular dynamics or non-linear wave equations. Our procedure rests on a decomposition of the spin Hamiltonian into a sum of two completely integrable Hamiltonians and on the corresponding Lie-Trotter decomposition of the time evolution operator. In order to make this method widely applicable we provide a large class of integrable spin systems whose time evolution consists of a sequence of rotations about fixed axes. We test the proposed symplectic integrator for small spin systems, including the model of a recently synthesized magnetic molecule, and compare the results for variants of different order.