[gmx-users] PME accuracy
vcb25 at cam.ac.uk
Tue May 6 12:22:00 CEST 2003
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%
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