Question on using fix nve/limit and langevin

LAMMPS LAMMPS Beginners
1

Dear all,

I used fix nve/limit and fix langevin to dissipate high-potential energies near the interfaces and relax the structures containg water and carbon molecules for few steps. The question here: should they be unfixed before performing nvt and nvt at following relaxation steps.
I read lammps documents and understand unfixing them leads to double integration. However, I get more logical results when I do not unfix fix nve/limit and langevin.

Is it correct to finialize the relaxation without unfixing these nve/limit and langevin?

2

No, it is an error. There must be no two fixes applying time integration or thermostatting to the same atoms. If you do the results will be bogus.

If your system does not behave well without fix nve/limit and fix langevin then either it is not yet sufficiently equilibrated or your simulation parameters (time step, interactions, force field styles and parameters, units, geometry) may not be suitable or plain bogus.