[gmx-users] background charge

Berk Hess gmx3 at hotmail.com
Wed Apr 4 10:47:46 CEST 2007

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.


>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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