[MMTK] H+ in water

Davide Ricci phd.davide.ricci at gmail.com
Tue Mar 20 15:32:48 UTC 2007


Thanks Konrad,
about this....you says that Ewald summation adds an uniform charge
background to the system, so that the total charge of the system is zero,
but you still have a proton in water for example. Is this done in an
automatic way ? Or we have to specify that we need a background charge to
neutralize the total charge ?

Bests
Davide

On 3/17/07, Konrad Hinsen <hinsen at cnrs-orleans.fr> wrote:
>
> On 16.03.2007, at 16:45, Davide Ricci wrote:
>
> > a stupid question...Suppose I want to study H+ in water, so that
> > the total charge of the system is +1. Can I do this in a Periodic
> > Universe in MMTK? Or Do I have to use a Finite Universe ?
>
> You can do that in a periodic universe. However, when you start
> calculating energies, you should be aware of the consequences. In
> principle, the energy of a charged periodic system is infinite.
> Depending on the electrostatics method chosen, there may be problems
> due to that, or unexpected effects. Ewald summation, for example,
> adds a uniform charge density to the system that neutralizes the
> total charge. That may or may not be what you want.
>
> Konrad.
> --
> ---------------------------------------------------------------------
> Konrad Hinsen
> Centre de Biophysique Moléculaire, CNRS Orléans
> Synchrotron Soleil - Division Expériences
> Saint Aubin - BP 48
> 91192 Gif sur Yvette Cedex, France
> Tel. +33-1 69 35 97 15
> E-Mail: hinsen at cnrs-orleans.fr
> ---------------------------------------------------------------------
>
>
>
>
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