AMBER Archive (2003)

Subject: Re: AMBER: NaCl ion pairs in TIP3P water box

From: Ioana Cozmuta (ioana_at_nas.nasa.gov)
Date: Wed Sep 24 2003 - 17:30:26 CDT

I did some simulations with KCl at 1M and SPC/M water for about 1ns. I've
started with two different configurations: the first in which ions are
randomly placed in the unit cell. The second in which I study crystal
dissolution. I end up with approximately same average behaviour thus I
think that at high concentration pairing and even clustering of ions is
not impossible and that's what some experimental chemist think as well.
It's a dynamic equilibrium however, not all the time the same ions
pair/cluster.

I also think that as long as we are unable to have a perfect model for
water, we will not be able to model that accurately ionic solutions
either. There are so many ff parameters for ions, some reproduce solvation
energies better, some transport properties. So at best what can be done at
the moment is to use the proper model for the purpose one wants to study.

Just a short personal opinion...

Ioana

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On Wed, 24 Sep 2003, Bill Ross wrote:

> Plus, the same-charge ion pairing occurs at 300K.
>
> Is there any evidence that ions don't pair in nature?
>
> Bill Ross
>
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