To see this, select first a random spin position x,y and assume that this spin and its nearest neighbors are all pointing up. The energy for this configuration is E=−4J. Now we flip this spin as shown below. The energy of the new configuration is E=4J, yielding ΔE=8J. E=−4J↑↑↑↑↑⟹E=4J↑↑↓↑↑ The four other possibilities are as follows E=−2J↑↓↑↑↑⟹E=2J↑↓↓↑↑ with ΔE=4J, E=0↑↓↑↑↓⟹E=0↑↓↓↑↓ with ΔE=0, E=2J↓↓↑↑↓⟹E=−2J↓↓↓↑↓ with ΔE=−4J and finally E=4J↓↓↑↓↓⟹E=−4J↓↓↓↓↓ with ΔE=−8J.