[gmx-users] PME accuracy

Bert de Groot bgroot at gwdg.de
Thu May 8 19:01:01 CEST 2003

Vincent Ballenegger wrote:

> In conclusion:  SETTING pme_order TO 4 LEADS TO VERY LARGE ERRORS IN THE

Somewhat worried by this statement (and the rest of the email), I performed 
two reruns (with pme_order 4 and 6) to calculate the electrostatic part
of the force on an ion in 200 MD snapshots (system: protein/lipids/water, 
approximately cubic box with ~80.000 particles). The differences for each component 
(and hence the sum) were very small: maximally 2 kJ/mol.nm (whereas the forces 
themselves have typical values of +/- 1000 kJ/mol.nm. 

So I don't know if the problems described by Vincent are particular to
his system (unshielded charges as far as I could see), but at least I was 
not able to reproduce the problem for a typical simulation system. 
(at least not to the extent described). 



Dr. Bert de Groot

Max Planck Institute for Biophysical Chemistry
Theoretical molecular biophysics group
Am Fassberg 11 
37077 Goettingen, Germany

tel: +49-551-2011306, fax: +49-551-2011089

email: bgroot at gwdg.de

More information about the gromacs.org_gmx-users mailing list