[gmx-users] a possible bug?

[Jim (Rui) Qiao]

Dear gmx-users:

I have tried out the newest Gromacs 3.3 last few days. I encountered a weird
problem, which I would like to report.

My system has one K+ and one Cl- ion located at (0,0,0) and (0,0,0.4)
respectively. I turned off the LJ interaction between them, so the only
thing left is electrostatics. To much of my surprise, the force acting on K+
is negative in the z-direction.

Could this be a possible bug, or is it a problem with my compilation (gcc
3.2.2, fftw 3.0.1, gromacs 3.3). I am attaching the source files, and wonder
if any of you could reproduce the results (you can simply type in: [grompp;
mdrun; gmxdump -f traj.trr |more], and look at the force acting on the first
atom).
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