[gmx-developers] TIP3P and TIP4P parameters

David spoel at xray.bmc.uu.se
Tue Jun 10 21:36:27 CEST 2003

On Wed, 2003-06-11 at 02:13, Erik Lindahl wrote:
> Hi Michael,
> I have no idea where the differences appeared, but to make things even 
> worse, these are the parameters I get from Bill Jorgensen's OPLS 
> datafiles when using the factor 4.184:
>   opls_111   OW     15.99940    -0.834       A    3.15061e-01  
> 6.36386e-01
>   opls_113   OW     15.99940     0.000       A    3.15365e-01  
> 6.48520e-01
> Yep, a third alternative - probably due to rounding in the opls 
> parameter file - at least I haven't done anything except applying the 
> conversion and using lots of extra digits for the accuracy.
> (These are the ones I sent to Eric Sorin in the updated OPLS files a 
> couple of months ago.)
> I agree that the published parameters is the best source, so I'll 
> change them to your values.

Although I agree that the published source is the best thing to follow,
at least for TIP4P Jorgensen has published at least two and possibly
three parameters. For instance the OW values above for TIP4P (opsl113)
is exactly what is used in Mahoney & Jorgensen (JCP 112, 8910, 2000).
TIP3P is also consistent with Mahoney, except that one digits is lacking
in the epsilon. Apparently Jorgensen has changed his definition of the
model without changing the name. So I'd vote for keeping the files
unchanged. We probably have to live with the fact that the force field
is a moving target.

Furthermore water properties for these simple models don't depend *that*
much on the exact parameters.
Groeten, David.
Dr. David van der Spoel, 	Dept. of Cell and Molecular Biology
Husargatan 3, Box 596,  	75124 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://xray.bmc.uu.se/~spoel

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