[gmx-users] oplsaa.ff parameters

[Eric Smoll]

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?

Best,
Eric