[gmx-users] oplsaa.ff parameters

[Barnett, James W]

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