[gmx-users] PME accuracy
Erik Lindahl
lindahl at stanford.edu
Tue May 6 18:33:00 CEST 2003
Hi Vincent,
First - the accuracy estimates are those of Darden and coworkers; check
out the Smooth PME paper mentioned in the references.
Second, I'll have a look both at PME and the normal (non-PME) fourier
method. We haven't used that for 1-2 years, so there might be a bug
there rather than in PME...
Cheers,
Erik
On Tuesday, May 6, 2003, at 03:21 America/Los_Angeles, Vincent
Ballenegger wrote:
> Vincent Ballenegger wrote:
>
>> * Ewald method with fourier_nx=25:
>> force = -10.824 "exact result"
>> * PME method with fourier_spacing=0.1, pme_order=4:
>> force = -7.789 error: 28% !!!
>
> I should have mentionned that the above figures were obtained with
> rcoulomb = 0.9.
> (The measured force is of course the projection of the force vector
> along the diagonal of the box.)
>
> Changing rcoulomb gives (for PME with fourier_spacing=0.1 and
> pme_order=4):
>
> rcoulomb=1.74 (~ half the box size) => force = -10.728 error: 1%
> rcoulomb=1.30 => force = -10.394 error: 4%
> rcoulomb=1.00 => force = -9.105 error:
> 16%
>
> Vincent
>
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------------------------------------------------------------------------
-----
Erik Lindahl, MSc, PhD <lindahl at stanford.edu>
D109, Fairchild Building
Dept. Structural Biology, Stanford University School of Medicine
Tel. 650-7250754 Fax. 650-7238464
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