[gmx-users] short and long range coulomb with pme

[nicolis at guideo.fr]

OK, thanks to both of you

> > No, the problem is that it isn't possible to separate group
> > contributions in the PME algorithm. I'm pretty sure it says that
> > somewhere in the manual too :-)

Yes, but as g_energy proposes to compute the group LR contributions I 
thought I had misunderstood the manual...
 
> Actually I just submitted a manuscript with a workaround. The trick is
> quite simple, you use tpbconv to make one group, e.g. the Ca++ have 
zero
> charge, and the you use the mdrun -rerun option to rerun your trajectory.
> Now you will get the PME energy for SOL-SOL. If you have multiple ions,
> you can then set the charges of the solvent to 0 and mdrun -rerun again.
> That will give you the PME energy for Ca-Ca.
> Now the interaction energy Ca-SOL is the difference between the 
original
> PME energy and that from the two reruns.

That's a very interesting workaround. Initially I was not interested in 
individual contributions, I wanted just check if I get something wrong. But I 
will maybe try it to see what gives.

Yiannis