[gmx-users] Could not converge NPT constraints

[juan-manuel.castillo at mv.uni-kl.de]

I have not much experience with Gromacs, although I have 
worked for years on molecular simulations. I am trying to 
run a NPT simulation of 1000 SPCE water molecules at 293 K 
with the opls force field. I equilibrated the system first 
during 1 ns using a velocity rescale thermostat, a 
Berendsen barostat, and a leap-frog integration method. 
Then I run a simulation using the md-vv-avek integration 
method, a Nose-Hoover thermostat, and a MTTK barostat. I 
have tried to change different parameters of the 
simulation, but after some steps I always obtain the 
following error:

Fatal error:
Could not converge NPT constraints

Anybody can help to explain what happens? I can provide 
input files if needed.