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

[Mark Abraham]

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.

It would be possible, but as manual section 4.6.2 says, you now create 
net dipole moments in your system. I can't think of a reason it 
shouldn't be fairly easy to increase this maximum of 32.

Mark