[gmx-users] error in hydrocarbon dihedrals of opls-aa?

[Markus Tusch]

Hi everybody,

I've just compared the following opls-aa torsional parameters for 
hydrocarbons given in J. Comp. Chem., Vol. 18, No. 16, 1955 - 1970 (1997)
as well as in J. Comp. Chem., Vol. 23, No. 15, 1416 - 1429 (2002)
with those in ffoplsaabon.itp (Gromacs 4.0.7):

##literature (these are also the original values for alkanes published 
by Jorgensen in 1996 I believe):
                     V1            V2            V3
H-C-C-H            0.0            0.0            0.318
H-C-C-C            0.0            0.0            0.366
C-C-C-C            1.74          -0.157          0.279

##ffoplsaabon.itp, keyword "hydrocarbon", (translated according to eq. 
4.64 of the manual):

                     V1            V2            V3
H-C-C-H            0.0            0.0            0.300
H-C-C-C            0.0            0.0            0.300
C-C-C-C            1.299          -0.05          0.200

There's obviously a difference.
Is there another source for the latter parameters which I just wasn't 
able to find? I know that the numbers in Gromacs were updated in 1999.

Cheers,
Markus

-- 
Markus Tusch M.Sc.
University of Paderborn
Faculty of Science
Department of Chemistry
Warburger Str. 100
D-33098 Paderborn
Germany

Tel. +49-5251-60-5754
e-mail mtusch at mail.upb.de