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

[Jose D Faraldo-Gomez]

>
> >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 :-)
>
>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.


But I thought that having a non-zero net charge in PME calculations wasn't a 
good idea... I mean, would the electrostatic energies be additive if one 
goes from a system that is originally neutral to a number of reduced 
subsystems which aren't?

Jose









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