TL;DR: In this paper, an isothermal-isobaric partition function of polymeric liquids was constructed by separating the local minima of the potential energy hypersurface from the anharmonic vibrations about these packings.
Abstract: We construct an isothermal–isobaric partition function of glass‐forming polymeric liquids by separating the local minima of the potential energy hypersurface from the anharmonic vibrations about these packings. The partition function is evaluated by a maximum term method. A suitable approximation to the partition function below a temperature T2 is required since the maximum term approach is not valid in this range of temperatures. We obtained the following results: (a) The density of states including thermodynamic quantities such as entropy and heat capacity reveal an Ehrenfest second‐order transition at T2; (b) T2