In the reverse Monte Carlo (RMC) modeling, there is no constraint of symmetry exerted on the model. Once the initial unit cell is expanded to a supercell, the symmetry constraint will be removed and the model will be purely driven by the data together with some other physical or chemical constraint. The purpose is to provide the model with as large configuration space as possible to explore and therefore it is hopeful that the model will be able to catch the distortion feature that is otherwise not accessible from the unit cell based routines. However, sometimes we may be still interested in the symmetry of the resulted supercell configuration from the RMC fitting. With this regard, the findsym program [1] developed by H. T. Stoles and B. J. Campbell, et al. could be used to extract the symmetry from a P1 cell.

There is an on-line version of the program available at [2]. Also, there is a command-line version of the program which can be found at [3]. The download is password protected, please get in touch with either myself (in which case I will get in touch with the developer for permission) or one can directly contact the developer for download.

To use the program, one can follow the process below.

Use the included findsym_cifinput program to generate the input file for running findsym.
```
./findsym_cifinput CIF_FILE_NAME.cif > CIF_FILE_NAME.inp
```
Grab the generated input file (CIF_FILE_NAME.inp in this example) and run findsym.
```
./findsym < CIF_FILE_NAME.inp > CIF_FILE_NAME.out
```
Most of the settings in the input file generated above should not need any retouching, apart from the tolerance settings as presented in the head part of the input file,
```
!useKeyWords
!title
CIF file mn3sn_500.cif
!latticeTolerance
 0.900E-04
!atomicPositionTolerance
 0.500E-01
!atomicPositionMaxTolerance
 0.330E+00
!occupationTolerance
 0.100E-02
...
```
The several tolerance settings here specify how tolerant we are for the various structure aspects. The more tolerant we are, the higher chance we will have to extract a higher symmetry, and vice versa. Imagine that we have zero tolerance, then a tiny amount of distortion from the ideal position or lattice parameter will be considered as lowering the symmetry and thus the extracted symmetry will tend to always end up with the P1 symmetry. In practice, one can play around with the tolerance settings and project a heat map to get a feel about the symmetry variation as the change of tolerance.

References

[1] H. T. Stokes and D. M. Hatch, J.Appl.Cryst.(2005).38,237-238.

[2] https://stokes.byu.edu/iso/findsym.php

[3] http://bit.ly/3seZjtR