The pair entropy is approximation to the entropy based on the pair distribution function g(r). We have used this quantity to define collective variables and fingerprints. You can find more details in the following pages:
This research is described in the following papers:
Enhancing entropy and enthalpy fluctuations to drive crystallization in atomistic simulations, Pablo Piaggi, Omar Valsson, and Michele Parrinello, Phys. Rev. Lett. 119 , 015701 (2017)
Predicting polymorphism in molecular crystals using orientational entropy, Pablo Piaggi and Michele Parrinello, Proc. Natl. Acad. Sci. USA 115 (41), 10251-10256 (2018)
Entropy based fingerprint for local crystalline order, Pablo Piaggi and Michele Parrinello, J. Chem. Phys. 147, 11, 114112 (2017)