Application of Intermolecular Potential-energy Functions

The same intermolecular potential-energy functions may be applied to correlate interaction virial coefficients. In the case where there are no, or insufficient, experimental data, but adequate data exist for the pure components, it may be possible to estimate with useful accuracy the unlike interaction parameters from combining rules such as  

The first of these relations is the Berthelot rule, and the second is the Lorentz rule. Combining rules are also required for other parameters in the chosen model. For example, the range parameter 2i2 in the unlike hard-core-square-well potential might be estimated as an arithmetic mean of 2n and (Table 3.3) 

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