[gmx-users] bug in ffoplsaanb.itp?

[Erik Lindahl]

Hi David,

On Mar 30, 2007, at 10:12 PM, David Mobley wrote:

> All,
>
> I'm looking at the epsilon value in ffoplsaanb.itp (i.e. from CVS of
> 3.3.1) for opls_400, F-. It's lilsted as 3.01248e00. This is roughly a
> factor of 10 larger than many of the other anions (i.e. Cl) and also
> roughly a factor of 10 larger than the AMBER96 value (in the same
> units) for F-: 2.552e-01.
>
> I assume that this is a typo in the opls file, and the correct value
> should be 3.01248e-01?

No, I don't think so, or at least it's not our typo :-)

It is quite common that ions end up with strange radii when you  
parametrize for free energy of solvation, and in addition those  
parameters are somewhat old (1984). Here's the extract from Bill  
Jorgensens file that we translated them automatically from:


400 09 F-   -1.0       2.73295   0.72000   F-  JACS 106, 903 (1984)
401 17 ??   -1.0       4.41724   0.11779   Cl- JACS 106, 903 (1984)
402 35 ??   -1.0       4.62376   0.09000   Br- JACS 107, 7793(1985)
404 03 Li    1.0       1.25992   6.25000   Li+ JACS 106, 903 (1984)
405 11 Na    1.0       1.89744   1.60714   Na+ JACS 106, 903 (1984)


You can probably figure out the columns yourself, but OPLS type 400  
has sigma=2.73295 and epsilon=0.72 (in angstroms and kcal units).  
I'll be happy to send you the entire file offline if you're interested.

Cheers,

Erik

PS: The constraint patch should be in CVS now, and the lambda-stuff  
is getting there!