[gmx-users] Electrostatic forces
dommert at icp.uni-stuttgart.de
Wed Jun 17 15:37:50 CEST 2009
* Berk Hess <gmx3 at hotmail.com> [2009-06-17 13:54:07 +0200]:
>I think there is still a general issue with optimizing the PME settings
>(or settings for any electrostatics method) for MD simulations.
>The question is what exactly one should optimize.
>If you do a single point calculation, you might only want to minimize
>the force error. But for MD you might also want good energy conservation.
>Optimizing the RMS force is certainly not the best choice,
>since that would lead to a large ewald_rtol, which gives small
>errors before the cut-off and on most of the long-range part,
>but large errors just beyond the cut-off. This will lead to bad
>energy conservation. Even an absolute force error will probably
>lead to a too large ewald_rtol.
increasing interpolation order and grid size, the optimal beta grows
and therefore ewald_rtol decreases. So increasing accuracy corresponds
to a descreasing rtol and finally optimized energy conservation. But
there arise other problems like a strongly differing charge density in
a simulation, that affects the error in the forces considerably.
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