Modified Mean Field approximation for the Ising Model

We study a modified mean-field approximation for the Ising Model in arbitrary dimension. Instead of taking a “central” spin, or a small “drop” of fluctuating spins coupled to the effective field of their nearest neighbors as in the Mean-Field or the Bethe-Peierls-Weiss methods, we take an infinite chain of fluctuating spins coupled to the mean field of the rest of the lattice. This results in a significative improvement of the Mean-Field approximation with a small extra effort.