[gmx-users] Question about the dihedrals in top file using OPLS force field in GROMACS

[Yanmei Song]

Hi,

I am using ffoplsaa.itp as my force field to do a simulation using GROMACS.
I have a question about how to write the parameters in dihedrals in
the itp file.

[ dihedrals ]
; ai  aj  ak  al  fu    c0, c1, m, ...
   1   2   5   6   1    0.0    3.77   3    0.0    3.77   3 ; dih   CAA
 CBF  OAW  CBH
   2   5   6   9   1    0.0    3.77   3    0.0    3.77   3 ; dih   CBF
 OAW  CBH  OAY
   5   6   9  10   1    0.0    3.77   3    0.0    3.77   3 ; dih   OAW
 CBH  OAY  CBJ
   6   9  10  13   1    0.0    3.77   3    0.0    3.77   3 ; dih   CBH
 OAY  CBJ  OBA
   9  10  13  14   1    0.0    3.77   3    0.0    3.77   3 ; dih   OAY
 CBJ  OBA  CBL

Then if I am choosing ffoplsaa.itp force field, what is the meaning
for c0,c1 and m under the [dihedrals]? Since i know that GROMOS and
OPLS force field have a different format for proper dihedrals. For
OPLS it seems there are four other parameter like v1 v2 v3 v4. Then my
question is how can i define the dihedral parameters in itp file based
on ffoplsaa force field in GROMACS? Thanks a lot!

Yanmei
-- 
Yanmei Song
Department of Chemical Engineering
ASU