  The previously developed n-vicinity method allows us to calculate accurately
critical values of inverse temperatures for Ising models with short-range
interaction. We generalize the method to the case of long-range interactions in
spin systems and obtain theoretical formulas for the inverse temperatures in
terms of the spin interaction constants. The comparison of our theoretical
estimates with computer simulations for the two- and three-dimensional Ising
models shows that the larger the dimension of the problem the better their
agreement.
