# spins_nnn¶

Classes

 SpinChainNNN(model_params) Spin-S sites coupled by (next-)nearest neighbour interactions on a GroupedSite. SpinChainNNN2(model_params) Spin-S sites coupled by next-nearest neighbour interactions.

Module description

Next-Nearest-neighbour spin-S models.

Uniform lattice of spin-S sites, coupled by next-nearest-neighbour interactions. We have two variants implementing the same hamiltonian. The SpinChainNNN uses the GroupedSite to keep it a NearestNeighborModel suitable for TEBD, while the SpinChainNNN2 just involves longer-range couplings in the MPO. The latter is preferable for pure DMRG calculations and avoids having to add each of the short range couplings twice for the grouped sites.

Note that you can also get a NearestNeighborModel for TEBD from the latter by using group_sites() and from_MPOModel(). An example for such a case is given in the file examples/c_tebd.py.