[gmx-users] Positive Coul. recip. term

Dommert Florian dommert at icp.uni-stuttgart.de
Fri Feb 24 08:17:45 CET 2012

On Thu, 2012-02-23 at 13:35 -0700, Denny Frost wrote:
> Dear all,
> I am trying to equilibrate a solvent of pure ionic liquid.  The system
> keeps exploding (after 2-5 ns) and I am not sure why, though I believe
> coulombic interactions are to blame.  This is because the Coul-SR term
> is negative, but the Coul. recip term is very positive throughout the
> entire run (giving the entire system a positive potential energy).  I
> think this means that the short-range electrostatics are okay, but the
> long range electrostatics (calculated with PME) are not.  Does anybody
> have any suggestions as to why this would happen?  I have used the
> exact same PME input parameters for another ionic liquid that works
> just fine.  They are listed below.
> rcoulomb = 1.2
> fourierspacing = 0.12
> pme_order = 4
> ewald_rtol = 1e-5

Depends on the force field you are using. Perhaps it ist not validated
for the ionic liquid you want to study. It is especially strange, that
it takes so long for your system to blow up. 

Moreoever I would try to optimize the PME settings with the tools,
g_tune_pme and g_pme_error, which give you performance and accuracy of
the parameters, respectively.

So perhaps with some more information I can provide more help.


> Thanks!
> Denzil Frost
> -- 
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Florian Dommert
Dipl. - Phys.

Institute for Computational Physics
University Stuttgart

Pfaffenwaldring 27
70569 Stuttgart

EMail: dommert at icp.uni-stuttgart.de
Homepage: http://www.icp.uni-stuttgart.de/~icp/Florian_Dommert

Tel.: +49 - (0)711 - 68563613
Fax.: +49 - (0)711 - 68563658
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