SpinChainXYZ

$H_{\rm XYZ}=-\sum_{i=1}^{N-1} \left( J_x S_{x,i}S_{x,i+1} + J_y S_{y,i}S_{y,i+1} + J_z S_{z,i}S_{z,i+1} \right) - J_x B \left(\prod_i \sigma_{z,i}\right) S_{x,N}S_{x,1} - J_y B \left(\prod_i \sigma_{z,i}\right) S_{y,N}S_{y,1} - J_z |B| S_{z,N}S_{z,1}$
where $B$ is the boundary condition (can be either 0,1 or -1).