The pair entropy fingerprint is described in the article "Entropy based fingerprint for local crystalline order". It can be used to distinguish between ordered and disordered atomic environments.
The fingerprint is implemented in the following codes:
Plumed: Not in the official repository. See instructions below.
Lammps: See the documentation here.
Pyscal: See the documentation here.
You can find the latest version of the Plumed implementation of the CV in this repository. The only file that you will need is src/multicolvar/PairEntropies.cpp .
This is a minimal input:
PAIRENTROPIES ...
LABEL=s2
SPECIES=1-250
MAXR=0.65
SIGMA=0.025
MEAN
... PAIRENTROPIES
This input will calculate the fingerprint for each atom in the group 1-250 and finally compute the mean of this values.