Researchers at Lyngby developed a three parameter temperature dependent form for the binary group energy interaction parameter to improve the UNIFAC method. The combinatorial part of the activity coefficient was also revised from the original UNIFAC equation.
The purpose of these modifications was to improve the accuracy of the UNIFAC method by accounting for temperature effects.
See "Modifications to UNIFAC" in the PRO/II Reference Manual, Volume I, Chapter 2, for additional information on this method.