Sunny

Status	Verified
Links	Docs, DOI, Github
Languages	Julia

Spin Hamiltonian

Sunny Hamiltonians will commonly have the format:

\[\mathcal{H} = \mu_{B}\mathbf{B} \cdot \sum_{i} g_{i}\mathbf{S}_{i} + \sum_{i<j} \mathbf{S}_{j} J_{ij} \mathbf{S}_{j} + \sum_{i}\sum_{k,q} c_{i,k,q} \mathcal{O}_{k,q} (\mathbf{S}_{i}).\]

The first term is Zeeman coupling to an external field \(\mathbf{B}\). The second term is a local bilinear exchange between dipoles. The third term is a single-ion anisotropy, which can be an arbitrary polynomial of spin. For example, this may be an arbitrary expansion in the Stevens operators \(\mathcal{O}_{k,q}(\mathbf{S})\). For details, see: sunnysuite.github.io/Sunny.jl/stable/renormalization.html

Sunny also allows to "toggle on" long-range dipole-dipole interactions with Ewald summation and arbitrary demagnetization tensor: sunnysuite.github.io/Sunny.jl/stable/library.html#Sunny.enable_dipole_dipole! It also allows for arbitrary coupling between pairs of sites \((i,j)\) as higher-order polynomials in \(\mathbf{S}_{i}\) and \(\mathbf{S}_{j}\) (e.g., scalar biquadratic, but more general pair couplings too): sunnysuite.github.io/Sunny.jl/stable/library.html#Sunny.set_pair_coupling!

Convention

Spin normalized	no
Multiple counting	no