I want to simulate an over damped non-equilibrium system similar to the active Brownian motion. I created many small molecule rigid bodies using fix rigid/small, each rigid body composed of three spheres. After reading the LAMMPS official website, I think fix brownian/sphere is very useful, but I am not sure if fix rigid/small can be used in conjunction with fix brownian/sphere. I see that the keywords are langevin, reinit, temp, etc. that follow fix rigid/small, but there is no brownian/sphere, so I am not sure if there is a problem with using fix rigid/small and fix brown/sphere together.
Those keywords have nothing to do with any fixes but have a specific meaning for fix rigid/small which is documented in the doc page of fix rigid/small
As a researcher, you should know how to apply “the scientific method™” to determine if there is a problem or not:
- set up a small test system with just one rigid body
- apply fix brownian/sphere as you intend
- determine up front what should happen and compare it to what does happen while paying close attention to the details provided in the documentation and watching the log file for relevant warnings or errors
- repeat this exercise with two and then more rigid bodies until you either run into unexpected behavior or have confirmed that you approach is viable
There are far too many permutations of combinations of options and command that can be used in LAMMPS for anybody to know in general up front if some combination of features is compatible or not.