Warren and Cowleys order parameter

For a solution containing molecules / and /, Warren and Cowley defined an order parameter r] j as being  

In the case of a binary mixture, therefore, we would have  

The two order parameters and are connected indeed, the number of pairs A-B can be expressed in two ways, such that  

If the coordination numbers of two types of molecules are the same in the solution (z = z b), then the two Warren-Cowley order parameters are also 

There is an obvious relation between the order parameters and the weighting factors ky- indeed, according to equations [3.51], [3.52], [3.62a] and [3.62b], we can write  

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