[gmx-users] How to deal with "non-zero total charge" problem in gromacs?

[sunyeping]

Dear all,

I am trying to do MD simulation with protein-DNA complex with gromacs. When using gmx grompp to generate the tpr file for energy minimization, I enconters a fatal error:

Fatal error:
Too many warnings (1).
If you are sure all warnings are harmless, use the -maxwarn option.

There are two notes and one warning arose with grompp, and they are:

NOTE 1 [file em.mdp]:
  With Verlet lists the optimal nstlist is >= 10, with GPUs >= 20. Note
  that with the Verlet scheme, nstlist has no effect on the accuracy of
  your simulation.
NOTE 2 [file topol.top, line 55]:
  System has non-zero total charge: -0.189598
  Total charge should normally be an integer. See
  http://www.gromacs.org/Documentation/Floating_Point_Arithmetic
  for discussion on how close it should be to an integer.
WARNING 1 [file topol.top, line 55]:
  You are using Ewald electrostatics in a system with net charge. This can
  lead to severe artifacts, such as ions moving into regions with low
  dielectric, due to the uniform background charge. We suggest to
  neutralize your system with counter ions, possibly in combination with a
  physiological salt concentration.

It seems that the -0.189598 non-zero charge causes the fatal error. Is it possible to correct it? and how? or could I use the -maxwarn option as mentioned in the error message?

Best regards