[gmx-users] oplsaa.ff parameters

[Eric Smoll]

Hello James,

Thank you for taking the time to respond to both of my OPLS-AA questions.
Your help is much appreciated.

Best,
Eric

On Sat, Sep 12, 2015 at 8:35 AM, Barnett, James W <jbarnet4 at tulane.edu>
wrote:

> On Thu, 2015-09-10 at 15:04 -0600, Eric Smoll wrote:
> > Hello GROMACS users,
> >
> > oplsaa.ff/ffbonded.itp contains the following line:
> >
> >   CT     CT     CT     CT      3      2.92880  -1.46440   0.20920
> > -1.67360
> >   0.00000   0.00000 ; hydrocarbon all-atom
> >
> > These values are at odds with those used provided in two publications
> > listed in "oplsaa.ff/forcefield.itp"
> >
> > W. L. Jorgensen, D. S. Maxwell, and J. Tirado-Rives, J. Am. Chem.
> > Soc. 118,
> > 11225-11236 (1996).
> > R. C. Rizzo and W. L. Jorgensen, J. Am. Chem. Soc. 121, 4827-4836
> > (1999).
> >
> > The fourier coefficients for "CT CT CT CT" (in kcal/mol) published in
> > the
> > above references are:
> >
> > V1 = +1.740
> > V2 =  -0.157
> > V3 = +0.279
> >
> > Using the conversion factors in the manual and a kcal-to-kJ
> > conversion
> > factor of 4.184
> >
> > C0 = F2 + 0.5*(F1 + F3)
> > C1 = 0.5*(-F1+3*F3)
> > C2 = -F2 + 4*F4
> > C3 = -2*F3
> > C4 = -4*F4
> > C5 = 0
> >
> > This evaluates to:
> >
> >   CT     CT     CT     CT      3     3.566860  -1.889076  0.656888
> >  -2.334672  0.000000  0.000000
> >
> > Is there a conversion factor I am missing?
>
> OPLS parameters for alkanes were updated in 2001:
> http://www.dx.doi.org/10.1002/jcc.1092
>
> --
> James “Wes” Barnett, Ph.D. Candidate
> Louisiana Board of Regents Fellow
>
> Chemical and Biomolecular Engineering
> Tulane University
> 341-B Lindy Boggs Center for Energy and Biotechnology
> 6823 St. Charles Ave
> New Orleans, Louisiana 70118-5674
> jbarnet4 at tulane.edu
> --
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