[gmx-developers] rlist, rcoulomb

David van der Spoel spoel at xray.bmc.uu.se
Thu Feb 12 07:22:46 CET 2009

Roland Schulz wrote:
> Hi,
> I understand why for cut-off, PME and RF the analytic formular does not 
> work for rlist>rcoulomb. As Berk pointed out in an earlier Thread this 
> would require an if statement. But couldn't it also be implemented with 
> a table? Thus, is there a reason why there is no table based function 
> for these three methods with F(r)=0 and V(r)=0 for rlist>rcoulomb?
For PME we actualy use a table. For cut-off and RF you can do it 
yourself, but you will introduce artifacts, since both V and F will be 
discontinuous in the case of a cut-off and F is discontinuous with RF 
(with epsilon_RF = infinity, otherwise V is discontinuous too). You can 
try a little water box with the table_12_6.xvg that is provided, but 
where you set everything beyond the cut-off to zero.
> Roland
> -- 
> ORNL/UT Center for Molecular Biophysics cmb.ornl.gov <http://cmb.ornl.gov>
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David van der Spoel, Ph.D., Professor of Biology
Molec. Biophys. group, Dept. of Cell & Molec. Biol., Uppsala University.
Box 596, 75124 Uppsala, Sweden. Phone:	+46184714205. Fax: +4618511755.
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://folding.bmc.uu.se

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