[gmx-users] dihedral potential

[manel.canales at upc.edu]

Dear friends

I'm very new in the gromacs world, and I have a very basic question:  
I'm interested to make simulations of polyaniline but using dihedral  
angle parameters different from those collected in the ffG53a6bon.itp  
bonded file force field. In this file the dihedral angle is always  
180. However the model that I would use says that the angle
is 163. The formula 4.60 (page 54 of  version 3.3 of the gromacs manual) says:

V = k*(1+cos(n*fi-fi0))

Therefore a fast solution could be to modify the ffG53a6bon.itp file  
replacing the fi0 =180 by the fi0 = 163. However I?m not really sure  
because I have read the paper where
this force field appears and in te paper fi0 is 180. If this is the  
case then ¿ I should solve the problem introducing dihedral harmonic  
restraints (formula 4.69 and 4.70 of the manual)  ?

Thank you very much for your help

Manel