Re: Solvation free energy difference of alchemical transformation of K+ into Na+

From: Hannes Loeffler (
Date: Mon Jan 09 2017 - 01:55:35 CST

You had and answer to your question just recently although the numbers
seem to be different. I think what you need to do is to engage in a
discussion to get an answer to your question rather than just repeat
your question a third time. In particular you would need to give at
least some detail as to what you have done. Otherwise it will be
difficult to find out where the problem is ... if there is any.

Your result appears to be quite ok compared to the one you cite. That
simple system must have been computed many times over and it is
certainly not enough to compare to just one source. So you probably
should look for other literature and get a feel how different such free
energies can be. Some reasons have been pointed out by the other
poster, e.g. force field. I would expect ions to be quite sensitive to

On Mon, 9 Jan 2017 11:39:32 +0530
Abhishek Kumar Singh <> wrote:

> Dear all,
> I'm alchemically transforming K+ into Na+ in a water box using
> CHARMM36 force field. I got the solvation free energy difference
> between K+ and Na+ -23.40 Kcal/mol while in one research publication
> (VB Luzhkov et al. Biochim Biophys Acta 1548 (2), 194-202. 2001 Aug
> 13) they have shown -17.33 Kcal/mol solvation free energy difference
> between K+ and Na+ using programme Q with GROMOS 87 force field.
> What can be the reason of this difference ?
> I appreciate your suggestions.
> ​Thanks,​

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