Sawtooth pattern when using run M every N after NPT command

LAMMPS LAMMPS General Discussion
1

bug_figure
bug_figure1920×987 194 KB

both versions: fix 1 all npt temp 50 2000 0.1 iso 0 0 2
red stars: run 150000
black circles: run 150000 every 50000 “write_data *.data”

These plots were generated from simulations using the 11Feb2026 version of LAMMPS. I saw the same results using the same scripts with the 22Jul2025 version of LAMMPS. Both versions have a plateau after the ramp from an NVE run after the temperature ramp.

Please let me know if there is way for me to send you the input scripts and log.lammps files used to generate this plot (if that would be helpful).

2

This is the documented and expected behavior.

The “every” option basically turn the single run command into multiple runs of 50000 steps duration each. Any ramp of a thermostat will reset for each (sub-)run command unless you use the “start” and “stop” keywords.