* Berk Hess <g...@hotmail.com> [2009-06-17 13:54:07 +0200]:
Hi, 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.
Hi, 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. Flo
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