Using fix shake with minimization

LAMMPS LAMMPS General Discussion
1

I am simulating a model of metal oxide and water in different versions of lammps. I am using TIP4P water model and using fix shake to keep the model rigid. When I am using fix shake before minimization, it is running fine on lammps-8Feb2023 but throwing error on lammps-23Jun2022 and other older versions of lammps(fix shake can’t be used with minimization). Any comment on this will be helpful.

2

If you need to use older versions of LAMMPS, just set the fix shake after the minimisation. There are no other options.

1 Like
3

If you are running minimization without fix shake, you must increase the force constants for the “shaken” bonds and angles to something like 100x larger than what the force field says. Otherwise, those bonds and angles may be deformed significantly and then starting the run with fix shake may fail due to being too far away from the constrained structure and the SHAKE equations not converging. This is what fix shake does automatically in the newer versions of LAMMPS when used during minimization.

1 Like
4

Thanks, Dr. Axel.