I recently installed the Sep 2021 build of LAMMPS, and built it with the EXTRA-FIX package enabled. I am trying to run a TTM simulation, however I am getting an error saying “Illegal fix ttm command (…/fix_ttm.cpp:100)”. This is also the case for the other versions of ttm such as grid and mod. I also see that there is a ttm file in both src, and in src/EXTRA-FIX. When I checked enabled packages using “make ps”, I saw a comment that says that the fix ttm in src is different than in EXTRA-FIX. The same file works on previous versions of LAMMPS with TTM. Do you know what may be causing this and a potential solution? Thanks!

Please carefully check the documentation. The fix ttm command has probably been revised since and some details of the command line have changed.

That was it. Thank you for the fast response!