[gmx-users] strange temperature coupling problem

Simple qsb at nlbmol.ibp.ac.cn
Fri Jan 13 05:07:03 CET 2006

Nickle Fan writed:
> Dear Gromacs users:
> I am having a rather strange problem in one of my simulation. The system
> consists of 2000 water molecules embedded between two walls. The wall atoms
> are position restrainted (force constant: 5000).
> The system is first equiliburated under NVT (Berendsen thermostat, tau_t =
> 0.1ps, Tsystem = 300K) for a while. Then I coupled the wall atoms to 300K
> (tau_t = 0.1 ps), and water to 300K (tau_t = 3000 ps). I found that during
I found you used (tau_t = 3000 ps) for water, I don't know why you use 
different tau_t for wall and water.But I think, under your setting, the 
temperature will only couple at  3000 ps interval. So in a 100ps simulation, 
the temperature of water would never adjust,Then the increasing of temp seem 
I'm not familiar with this problem.I only notice the strange setting, maybe 
there are other opinions, 
> a 100ps simulation, the temperature of water rise continuously to 400K!
> (the wall atoms are OK though). I tried to disable water temperature
> coupling by set tau_t = 0 for water, but it does not help.
> I tried NVE simulation from the same initial configuration, and it appears
> that the temperature of water during the first 50 ps is about 300K. So we
> can rule out the possibility of bad local contact in the system. Then what
> could possibly goes wrong with the system?
> I  am using PME (4th order), vdw-type = Shift, rvdw-switch  = 0, rvdw =
> 1.1, rlist = 1.2. Time step is 1fs.
> Any help would be greatly appreciated.
> Nick Fan

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