The Ising model without temperature—A possible explanation for the critical energy of the Onsager solution

The internal energy u and the entropy S are used to describe the low and high temperature behavior of simple Ising systems. From the different types of degeneracy, bond occupation as realized by the linear chain is applied to open nets with weighting factors, which are used to optimize the internal energy u near the state of total disorder at u=0. The resulting linear programming problem describes correctly the behavior of S(u) near u=0, and allows to explain for the periodic square net the critical energy uc of the Onsager–Kaufmann solution and the occurrence of the logarithmic singularity at uc.