Binary interaction parameter (BIP) is a constant that accounts for the deviation from ideality for two component mixtures. BIPs are specific to one equation of state as they are calculated by regression of measured data.
For example, coefficients used for peng robinson equation of state (EOS) are different from those used in Soave-Redlich-Kwong (EOS). The coefficients used in a liquid activity method are essentially regression constants used to calculate the liquid activity coefficient.
