Thanks, that's a good point. I was unhappy with the ~30K temperature
fluctuations that I was getting in my thousand-atom system with tdamp >
timestep, but I suppose up-sizing would help there, and if not, I'll turn to
you are probably quite a bit away from equilibrium.
i would run for a bit with nve plus langevin until things
settle and then switch to nvt without reinitializing the
velocities, of course.
if you still get large fluctuations in the kinetic energy,
then i would use the drag flag to dampen them, but
they may be intrinsic. you should be able to test that
by doubling the system and checking if the fluctuation
will be smaller.
Any thoughts on the Pdamp problem? I get immense pressure fluctuations with
reasonable values of Pdamp, but maybe again that's because of the size of my
same question: are you sure you are well equilibrated?
if you have large volume fluctuations due to the pressure
fluctuations, then you will of course need to rebuild the
neighbor lists a lot, and if you have too large a delay
value, you'll get dangerous builds, or may need to reduce
the time step. for solids like quartz, you should expect
quite large pressure fluctuations. the damp feature was
implemented exactly that under control.
i would still recommend to first equilibrate with fixed
volume before switching to npt.