[gmx-users] background charge

[Berk Hess]

There have been several discussions on counterions
PME background charge. Please search the mailing list.

If you want to mimick infinite dilution, you probably
do not want to add a counter ion.

Reaction-field makes the same uniform background charge
assumption as PME. But RF is actually worse, because
the uniform background charge is applied individually
to the cut-off sphere around each charge-group, instead
of to the whole system.

Berk.

>From: baloilgiullare at interfree.it
>Reply-To: baloilgiullare at interfree.it,Discussion list for GROMACS users 
><gmx-users at gromacs.org>
>To: gmx-users at gromacs.org
>Subject: [gmx-users] background charge
>Date: 3 Apr 2007 17:28:16 -0000
>
>I have a question about simulating metal ions in aqueous
>solution at an infinite diluition: say I have a metal ion
>(such as Ca2+ or Mg2+) and about a thousand water molecules.
>I have to compensate the non zero charge of the system
>with negative ions?
>As I can understand the use of a reaction field can account for this fact
>and exist water models with force fields parametrized ad-hoc
>(J. Chem. Phys. 108,10220 (1998)).
>How about methods like Ewald or PME if I have a nonzero total charge?
>And if I need not use use long range electrostatics at all?
>
>Thank you in advance
>
>Vincenzo Moreschini
>
>
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