[gmx-users] problem with the max number of atom in charge group

[David van der Spoel]

Nicolas Sapay wrote:
> Hello everybody,
> 
> I'm trying to use a DPPC bilayers with charges from the Jacob Sonne et 
> al. study (Biophys J., 2007). The problem is that the authors have 
> defined a single group for the whole DPPC molecule. This allow them to 
> define new accurate charge for the head group atoms and the first atoms 
> of the acyl chains. It is a problem with Gromacs which tolerate only 32 
> atoms per group (When I try to minimize my system, I've got the error : 
> Max #atoms in a charge group...). In Gromacs, is it possible to defined 
> groups with a net charge different form an integer, like 0.026042? Would 
> it be a problem if I use PME? Note that the net charge of the molecule 
> is still zero, of course.
> 
> Thanks
> 
> Nicolas
> 
> 
If you use PME than this is perfectly fine. You do not want charge 
groups larger than 3-4 atoms because the charge group is also used for 
neighborsearching, that means LJ interactions are between whole charge 
groups as well.

-- 
David.
________________________________________________________________________
David van der Spoel, PhD, Assoc. Prof., Molecular Biophysics group,
Dept. of Cell and Molecular Biology, Uppsala University.
Husargatan 3, Box 596,  	75124 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://folding.bmc.uu.se
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