[gmx-users] OPLS-AA forcefield for perfluoroalkanes

[Pedro Morgado]

Dear all,

I am currently simulating perfluoroalkanes with gromacs, and I have
detected that the parameters for the F-C-C-F dihedral in the opls-aa
parameter file (ffbonded.itp) do not match the parameters published in the
original Watkins and Jorgensen paper (J. Phys. Chem. A 2001, 105 (16),
4118–4125.).
In more detail, the parameter file has the RB coefficients: [-5.23 5.23 0.0
0.0 0.0 0.0], instead of [-4.707 6.799 0.0 -2.092 0.0 0.0], which result
from the conversion of the parameters in Watkins' paper from Fourier to RB
form and from kCal to kJ.

Does anyone know if there is a reason for this difference (perhaps a typo
in the published paper)? Or if this is just an error in the parameter file?

Thank you,
Pedro Morgado