[gmx-users] Electrostatic forces

[Florian Dommert]

* Berk Hess <gmx3 at 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

>
>Berk
>
>
>_________________________________________________________________
>See all the ways you can stay connected to friends and family
>http://www.microsoft.com/windows/windowslive/default.aspx
>_______________________________________________
>gmx-users mailing list    gmx-users at gromacs.org
>http://lists.gromacs.org/mailman/listinfo/gmx-users
>Please search the archive at http://www.gromacs.org/search before posting!
>Please don't post (un)subscribe requests to the list. Use the 
>www interface or send it to gmx-users-request at gromacs.org.
>Can't post? Read http://www.gromacs.org/mailing_lists/users.php

-- 
Florian Dommert
Dipl.-Phys.

Institute for Computational Physics
University Stuttgart

Pfaffenwaldring 27
70569 Stuttgart

Tel: +49 - 711 / 6856-3613
Fax: +49 - 711 / 6856-3658

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

!! PGP-ENCODED emails preferred !!
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 194 bytes
Desc: not available
URL: <http://maillist.sys.kth.se/pipermail/gromacs.org_gmx-users/attachments/20090617/5a5c2d6c/attachment.sig>