Near-neighbour correlations Bethes method

CJearly near-neighbour correlations have to be allowed for in the molecular statistical approach to give a better description of the pretransition effects. A step in this direction was taken in which 

6 Near-neighbour correlations Bethe s method 2.6.1 The Krieger-Jantes approximation 

The theory is based on a method developed originally by Bethe for treating order-disorder effects in binary alloys. We suppose that every molecule is surrounded by z neighbours (z 3) and that no two of the z neighbours are nearest neighbours of each other. (This implies that in writing down the interactions between the central molecule and its z 

The relative probability of the central molecule assuming a certain orientation 0d, v o is 

If we postulate that these two probabilities are identical when 0 and 1 have the same orientation, we obtain the following consistency relation due to Chang 

---