Hi,
I work with Grayson Streed Thermodynamic model and I have heard about two improvements :
1 - Erbar Modification Grayson Streed (named GSE)
2 - Improved Grayson Streed (named IGS)
For the first one, I have found only one reference:
Erbar J.H., Edmister W.C.
Vapour-Liquid Equilibria...