From nearest neighbor couplings, the difference in energy between all spins equal and staggered spins is 8 J. The difference in energy between all spins equal and nonstaggered but net zero spin is 4 J. Ignoring four-spin interactions, a reasonable truncation is the average of these two energies or 6 J. Since each link will contribute to two odd spins, the right value to compare with the previous one is half that: 3 J ′ = ln ⁡ ⁡ ( cosh ⁡ ⁡ [ 4 J ] ) .