Fix halt freezes or causes dynamic group error


I am trying to use the “fix halt” command to stop a run after a condition is met (20% crosslinking) and then continue with the rest of the LAMMPS input code, but I think I have encountered a bug. When I run on windows with LAMMPS version 8 Feb 2019, the following error occurs after the halt condition is met: “Per-atom property for group dynamic does not exist.” When I run on Linux HPC with LAMMPS version 12 Dec 2018, it stops the run after the condition met, but the simulation does not continue to the next line, it does not display an error, and it never exits (it continues to “run” but nothing further is output to the log file).

I have already successfully used the halt command to stop/continue after a certain density is reached, but I cannot figure out why it will not work in this situation. Because it responds differently to different versions of LAMMPS, I think it may be some sort of bug. I reduced the input file to a fairly simple test that should stop after 20% crosslinking as attained. It runs in a few seconds. I have attached the necessary files.

I could not find any information addressing this problem on the documentation or the mailing list, and I would greatly appreciate some help with this issue.

Also, the documentation seems to suggest that fix halt is meant to be used as a troubleshooting tool rather than for breaking out of a run after a desired condition is met. Is there any reason not to use it for this kind of purpose? Or is there more preferred approach?

Thank you very much for your time.


Jacob Schichtel (271 Bytes) (233 Bytes)

center_postreact.template (4.08 KB)

center_prereact.template (3.11 KB)

edge1_postreact.template (3.07 KB)

edge1_prereact.template (2.12 KB) (277 Bytes)

edge2_postreact.template (4.3 KB)

edge2_prereact.template (3.45 KB) (992 KB)

LAMMPS_crosslink.lmp (3.46 KB)


this doesn’t look to me like an issue with fix halt, but an issue with fix bond/react. the latter fix is under active development and thus different LAMMPS versions may show different behavior.


Hi Jake,

Please try adding these commands after you ‘unfix’ bond/react:

group nonreactgroup_REACT delete
group bond_react_MASTER_group delete

I am now realizing this should probably be done automatically by fix bond/react.



Hi Jake,

Thank you for the suggestion! It did indeed work for the latest version of LAMMPS (28 Feb 2019).



PS I am very appreciative of your bond/react command.