[gmx-developers] Re: TIP3P and TIP4P parameters

[David van der Spoel]

On Thu, 2003-06-12 at 06:23, Erik Lindahl wrote:
> Yep.
> 
> In theory we could of course use the exact C6/C12 values in the 
> forcefields that specify the parameters that way, but I'm not too 
> enthusiastic about the idea of getting slightly different TIP3P 
> parameters depending on whether you selected Gromos96/OPLS/Amber for a 
> forcefield... asking them seems like a good idea - if nothing else to 
> make sure we use the same values as the model authors.

I do have a vague recollection that TIP4P has changed from the original
somewhere in the late 1980's, I haven't however been able to find a
reference. Maybe this one:

@Article{Jorgensen88,
  author =       "W. L. Jorgensen and J. Tirado-Rives",
  title =        "The {OPLS} Potential Functions for Proteins. Energy
                 Minimizations for Crystals of Cyclic Peptides and
                 Crambin",
  journal =      {J. Am. Chem. SOc.},
  year =         "1988",
  volume =       "110",
  pages =        "1657--1666",
}

> 
> 
> Cheers,
> 
> Erik
> 
> On Wednesday, June 11, 2003, at 09:03  PM, Michael Shirts wrote:
> 
> >
> > OK, let me write this all out. The problem comes from the fact that the
> > original defintions of TIP3P and TIP4P in the 1983 paper in the 
> > previous
> > e-mail come from the equation:
> >
> > U = A/r^12 - C/r^6
> >
> > For TIP3P, the constants are A = 5.820 x 10^5, C = 5.950 x 10^2
> > For TIP4P, the constants are A = 6.000 x 10^5, C = 6.100 x 10^2
> >
> > Whereas later papers use the form:
> >
> > U = 4*eps*[(sigma/r)^12 + (sigma/r)^6]
> >
> > The original paper's values for A and C yield:
> >
> > TIP3P:
> > eps = 3.1505651 A     sig = 0.1520725 kcal/mol
> > eps = 0.31505651 nm   sig = 0.6362713 kj/mol
> >
> > TIP4P:
> > eps = 3.1535779 A     sig = 0.1550416 kcal/mol
> > eps = 0.31535779 nm   sig = 0.6489640 kj/mol
> >
> > In at least one later paper (Mahoney and Jorgensen, jcp, vol 122 no. 
> > 20, 22
> > May 2000, p. 8910), these parameters are listed as:
> >
> > TIP3P:
> > sig = 3.15061 A       eps = 0.1521 kcal/mol
> >
> > TIP4P:
> > sig = 3.15365 A       eps = 0.1550 kcal/mol
> >
> > Clearly there has been rounding, in both the sigma and the epsilon.  
> > Though
> > the sigma results are a litle strange even then . . .  I've checked 
> > these
> > several times, but if somebody else would once more just to be sure, 
> > it would
> > be nice.
> >
> > I'll do some test to try to figure out how much difference these 
> > changes could
> > make. Perhaps I'll send an e-mail to Jorgensen and/or Madura about it 
> > once I
> > run those tests . . .
> >
> > Cheers,
> > Michael
> >
> >
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-- 
David van der Spoel <spoel at xray.bmc.uu.se>