[lammps-users] Question about "drag" argument in Fix NVT

Dear all, I want to equilibriate some structure in some temperature using NVT ensemble, I tried several “drag” values, but the temperature still fluctuates a lot ( 100 k), I am wondering how I can keep the tempeature reasonably constant?

Many thanks.

Dear all, I want to equilibriate some structure in some temperature using
NVT ensemble, I tried several "drag" values, but the temperature still
fluctuates a lot ( 100 k), I am wondering how I can keep the tempeature
reasonably constant?

there are a ton of reasons for those fluctuations.

please post an example input, then people here don't have
to guess about the cause.

in most cases the fluctuations are either due to an
error elsewhere or actually physical.

if you are far from equilibrium, you might be better off
using "fix nve" and "fix berendsen" until your total energy
remains fairly constant and then switch to "fix nvt".

cheers,
   axel.

If you start with an equilibrated system and set its intiial Temp
to a value, then you should be able to run with any thermostat
in LAMMPS and not get big fluctuations. If you can't then something
isn't equilibrated and NVT will have fluctuation problems.

Steve