The Twu Peng-Robinson Equation of State is described in:
C.H. Twu, J.E. Coon, and J.R. Cunningham, "A New Cubic Equation of State," Fluid Phase Equilib., 1992, 75, 65-79. C.H. Twu, D. Bluck, J.R. Cunningham, and J.E. Coon, "A Cubic Equation of State with a New Alpha Function and a New Mixing Rule," Fluid Phase Equilib., 1991, 69, 33-50.
Details of the equation implementation in TDE are provided here Parameters determined in TDE are:
critical temperature: Tc, critical pressure: pc, acentric factor: w, parameters L, M, and N, and the volume translation term: vt