Theory of the frustration effect. II. Ising spins on a square lattice

For pt.I see Commun. Phys., vol.2, p.115 (1977). Presents numerical results for the ground-state properties of the simplest system showing the frustration effect, Ising spins on a square lattice with a variable concentration x of antiferromagnetic interactions. Ferromagnetism disappears at a concentration xc approximately 0.09. The ground-state energy and degeneracy have markedly different behaviours below and above xc. The authors compare the results with other calculations and stress the advantages of the frustration approach.