[MMTK] Ewald summation parameters

Berit Hinnemann Berit.Hinnemann@fysik.dtu.dk
Wed, 10 Jul 2002 12:13:46 +0200

Hi Konrad,

I'd like to ask something about the Ewald summation parameters "beta",
"real_cutoff" and "reciprocal_cutoff". In the file
NonBondedInteractions.py I found how they are calculated from the system
size and so far I used those parameters for my calculations.

Where do these estimation expressions come from (could you maybe point
out a reference)? Do they work for most systems? I'd like to test and
optimize the parameters for my systems, but I don't know what they mean.
Is it right that

-the bigger beta, the more precise the calculation (or how should beta
be chosen)
-the bigger real_cutoff, the more precise the calculation
-the smaller reciprocal_cutoff, the more precise (you actually write
that in the manual, I think)

The energies I obtain with the default parameters are very reasonable,
so I don't have any reason to suspect that they don't work. I just want
to make sure.
Thanks a lot for any hints.

Best regards,

Berit Hinnemann
Center for Atomic-Scale Materials Physics (CAMP)
Dept. of Physics, Technical University of Denmark
Building 307, DK-2800 Lyngby, Denmark 
Phone: +45 4525 3209, Fax: +45 4593 2399