[gmx-users] ns_type=grid leads to blowups in minimization but not with ns_type=simple

[David Mobley]

Dear all,

I've been having some very sporadic problems with minimization (that
is, only on some of the many systems I minimize). In some cases,
during steepest descent minimization (following L-BFGS, which
essentially ends immediately for the system in question), minimization
runs for about 10 steps, and then I get an error about a water
molecule that couldn't be settled, followed by the following:

Range checking error:
Explanation: During neighborsearching, we assign each particle to a grid
based on its coordinates. If your system contains collisions or parameter
errors that give particles very high velocities you might end up with some
coordinates being +-Infinity or NaN (not-a-number). Obviously, we cannot
put these on a grid, so this is usually where we detect those errors.
Make sure your system is properly energy-minimized and that the potential
energy seems reasonable before trying again.

Variable ci has value -2147483648. It should have been within [ 0 .. 1521 ]
Please report this to the mailing list (gmx-users at gromacs.org)


Strangely enough, if I switch ns_type from grid to simple, everything
seems to work fine.

Does anyone have any idea why this might be? Is there some reason
ns_type=grid shouldn't work right for minimization? Or is there a bug?
(I can submit a bugzilla with input files and so on, but first I
wanted to make sure I'm not doing something stupid).

Thanks,
David