XX model on the circle
  We diagonalize the XX model with a finite number of spins and periodic boundary conditions. We solve for the ground state, focus on the rapidity of the convergence to the thermodynamic limit and study the features of multipartite entanglement. 
A. De Pasquale, G. Costantini, P. Facchi, G. Florio, S. Pascazio, K.   Yuasa