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

[Erik Lindahl]

David van der Spoel wrote:

>On Mon, 29 Apr 2002, Erik Lindahl wrote:
>
>>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.
>
That's a smarter solution when it works, since you won't have to do the 
extra calculation every step, but just use do it for the frames in the 
trajectory.

Cheers,

Erik